Are there any spare parts on board??? Ikelite users probably use the same C Clip?? if not you might get buy with placing a proper fitting washer on the shaft and then twisting some fine wire in the grove where the C clip is supposed to be. I hope you have the rubber / vinyl cap also. this may work.
Also if you don't need the button or another button remove the button, remove the spring reinsert the button and either use the wire or tape solution you suggested.
A vacuum system would also help but it may pull the button in and activate that function on the camera.
best of luck, I am sure you will have spare C clips on the next trip.
- DiverPam likes this