Well, you're going to lose muscle strength, and you're going to lose some aerobic capacity. A few thoughts:
* Ask when/whether it's possible to swim. If you can, that could help.
* Some circuit training with upper body only may give you some nice cardio workout, if you can work between the machines.
* Put your bike on a trainer, and take one pedal off? Might give you a weird imbalance.
* Some gyms have a arm/pedal trainer...
* Is rowing on an erg weight bearing?