The problem has always been there was no mechanisms to actually implement the ideas in High Guard.
Three ideas I had were somewhat similar.
1. The default fuel tanks have a piston that moves inward as the tanks empty, which, of course, reduces volume; since the tanks are empty before transition, jump calculations are based on the resultant negative volume.
2. Pop up tanks, though you'd have to ensure that the pop up mechanism doesn't permit leakage.
3. Simplified collapse, in that one of the walls of the tank, usually the roof, opens up.