If you need a definite answer, let me know, I have electrical diagrams for this car somewhere.
A few ideas, let me know what soounds best to you:
The radio on yours should have speed-dependent volume control, and there is a signal wire into the radio to control that, so this may work, if you can remove the radio (special tool "keys" required to remove the radio).
The speedo receives it's speed signal from the traction control module (I believe yours has traction control, if not, then it would come from the ABS control module). The control module receives all the speed signal, but on this, the signal processed to the speedo and other systems requiring a speed signal is processed off of the left front wheel.
There also may be a speed signal "bus" or terminal in the car someplace you could tap in to.