I think William's suggestion is the most practical solution. It's not that hard, and I use open flash technique with lenses that have no shutter or an unsynched shutter.
The idea of modifying a shutter for sync at the end of the flash is an interesting one. The X-sync mechanism is just a simple switch. You might try it with some older shutter that is easier to work on, like an Ilex, rather than a modern shutter which is much more complex. Normally, on X-sync, the flash fires when the shutter is all the way open. You would need to locate the mechanism that closes the shutter and build a sync switch into it so that the flash would be fired just before the shutter closed. I think there is an Ed Romney book on repairing older shutters. Maybe study that, and see what you can rig up.