Tom,
I had an exact same situation before. What I did was; I made up a dummy wheel by lacing non gear side flange as normal way, BUT used #14 spokes hooked into openings of the kidney shape holes. (Do not have to tighten much, just balance the tension to the other side)
In this way, you can re-distrubute Force of freewheel extraction to overall flange, and thus not to damage the precious large flange!
Warmest Regards,
KEN TODA, kept buying Campy H/F Record Hubs, so all my wheels C-H/F hubs!