This won't really help, but I bought a wireless and attached it to the rear wheel, but if the wire is long enough you may be able to route the sensor/cable back to your rear wheel and zip tie it in place along the frame. Some trainers have computers that work with them, but that's specific to the trainer, so not sure what options your particular model might have.

Before I got my computer I would go about a half hour at a pretty steady high tempo pace and because my trainer is a fairly "budget" mag trainer, I would have the bike in the biggest gear in order to max resistance for a decent workout.

Shannon