You could use something like a giant mux (double throw, or single-throw with all the motors having a single common ground connection). BUt this would be a very big, very high power mux that you woudl have to manually build. By the time you finished (especially if it's a solid state mux), then you'd have pretty much built an H-bridge that MUST be cascaded into your original H-bridge. You might as well just build 5 more H-bridges.
And it would not stop the motors that aren't being controlled form drooping and losing position.
If you are thinking about making the H-bridge quickly refresh the position of each motor and then jump to the next one, this would involve 1/6th the holding power the H-bridge is capable of, or 6x the switching speed which would overheat the H-bridge. The switching speed required for this also necessitates a solid-state mux (and not simple relays) which defeats the purpose because the work of building such a solid-state mux would be the exact same work involved in building more H-bridges.
THe onyl situtation where it might be feasible to do anything really is if these were servo motors that were driving worm gears that would hold their position unpowered. You could mux the feedback signals along with the motor power. And you'd have to use relays because the additional work would be minimal and simple. As soon as you build a solid-state mux, you need gate drive and protection circuitry which would be exactly as if you built more H-bridges.