I too have occasion to adapt other tools to bike use and to make or alter other tools. Here are a couple of them.
1. Chain third hand. When "breaking" a chain I use a piece of an old spoke bent in an elongated C shape on its back. Starting with a spoke piece about 8" long with one inch "hooks" bent length about 6 inches long after being bent. This is hooked through a link of the chain on either side of the break to keep the chain open ends close together without tension. The reason is to allow using the chain tool, without also trying to grow another hand, or without all my attention on keeping the chair together while I rejoin it. Essentially a third hand for a chain. I am relatively sure most people know about doing this. I toss it in anyway.
2. Crankset third hand: This is for removing the fixed cup with the spindle still in. It holds the wrench in place so you can use a hammer when that is a necessity. I use 2 large fender washers because they are thin(which is an automotive type washer originally; it has a much smaller hole that the outside of the washer would usually have). The outside diameter of the washer must be larger than the cup diameter or at least as large as the BB, the holes must be large enough for the spindle to fit through. The large washers are spot welded, epoxied, taped, or whatever you wish to use to keep it attached to a large nut. The large nut must also be large enough inside diameter for the spindle to fit through. On the opposite side of the nut from the first washers attach two smaller washers, Two because of their thinness. The outside diameter at least as large as the outside diameter of the nut. The hole diameter large enough for a BB crank bolt to fit through. I do not use the crank bolt however it is usually not long enough. I get a replacement bolt of same diameter and threading but about 1/2" or 3 cm longer than the crank bolt. How to use: The wrench to remove the fixed cup is put in place as if you were going to remove the cup. The wrench is difficult to keep in place when it is necessary to use a hammer to persuade the cup to turn. The nut-washers assembly is place over the spindle with the large washers "clamping" the wrench against the edge of the BB. The bolt is put through the small washer hole and is screwed into the end of the spindle. It does not require anything beyond finger tightening. You will have a sandwich of; Bottom Bracket-removal wrench-large washer(s)-large nut-smaller washers and bolt holding all of this on top the spindle. The wrench may then have a hammer applied to it without fear of it flying and injuring someone or flying and injuring a lovely painted surface.
3. fixed cup remover: I use this when the spindle has been removed. I use a coarse thread bolt large enough to barely fit through the spindle hole. I use a small washer on either side of the cup. A nut for the bolt is then screwed on the nut is in the bottom bracket, the bolt head outside the bottom bracket. A socket wrench to fit the bolt head is used with a large breaker bar or long ratchet arm. The bolt is then tightened down and because the cup is left hand threaded, the bolt nut combination tightens down and as you turn the ratchet or breaker clockwise to tighten the bolt the cup is loosened. I have always feared breaking a cup but I not broken one as yet. I prefer this to the wrench third hand. Hammers can be dangerous.
4. Tire Tools: I have used motorcycle tire irons for years to remove and replace tires. They are quite a bit longer than the little irons in a road repair kit. they do not have the spoke hooks but this has never been a problem for me.
5. VAR lockring tool: I have two of these and use the extra one for removing and replacing brass pop-up sprinklers in my yard. They are an expensive sprinkler tool, but I have had them forever and they were cheaper then.
6. I use medical forceps for placing loose balls when servicing bearings. I prefer the curved ones of 6" to 8".
7. I use never-seize when putting threaded object together. It is the brand name for an anti seize compound. I find metals exposed to the elements sometimes try to become one single piece. It is probably not suitable as a lubricant.
8. Seals: I have used O-rings for seals where I felt I needed a bit more weather exclusion on old non-sealed rotating bike parts.
I am no rocket scientist and it is highly likely you already have a way of doing what you need to do on your bike. I have just had a few necessities where I had more time than money or the repair always needs to done when no shop is open.
John Strizek
Sacratomato California USA