Kevin,
I personally wouldn't worry about it and I never heard this as an issue. There are many, many places on a bike where Al and chromed steel are in constant contact with no apparent ill-effects. Now if you leave bike in the wet or store in the channel, I'd bet electrolysis could become an issue. If you insist on being concerned, perhaps a light coat of grease or friction-tape at contact point may minimize reaction but then bar slippage could be a greater problem.
Jack Romans
Sacramento, California