I don't think it's possible. but, I do like a challenge! Remove the bath panel and the bath legs, see if the sealant around the bath holds the bath up. If so multitool around the edges of the rotten floor. If you angle the blade of the multitool sideways you should be able to do it, it'll be tricky and annoying with the restricted space but possibly could be done. Then pva the edges of the floor that was rotting (they would still be wet and rotting and don't want that moisture passing into the new floor and it should just dry out if not too damaged already. Replace then floor with chipboard. You might have to do it in 2 halves if when you remove the legs the bath starts to drop, so maybe remove 1 leg do that bit of floor, then the next. Fuck knows, worth a try.