dumbest trainer question ever

That's not a stupid question.  Hmm, not sure if moving the magnet and sensor to the back tire would work...maybe if it were wireless it might work, but corded would be a real pain and may not even reach. 

Personally I use my Garmin 305 with a cadence/speed sensor (bought separately from the 305 unit).

Move it to the back if possible.

Cadence is very important while using a trainer.  If you don't have a cadence sensor, consider upgrading to a new computer with cadence and speed. 

Wheel speed on a trainer isn't going to translate to road speed.  Rolling and wind resistance are completely different.

Your best bet, to determine how good of a workout you're getting on a trainer is to use a HR monitor or a power meter, and focus on that instead. 

I don't worry about the speed on my trainer. i use HR and time on the seat.    

plus it would suck to see that i'm rolling at like 30mph and going no where. lol

I use my 305, because of the speed and cadence sensor that I bought for it, but I use it for the speed, time and distance that I go on my rollers.  No, it is not the same as having a 20 mph wind in your face or climbing hills but from a workout comparison the rollers seem to be closer to an actual road workout than a trainer is for me.  I own both, but really like my rollers that are just about shot.