The problem is that the computer is wireless and the distance from the crank to the computer seems to be too far--by about 2-3 inches! Is there any way to 'boost' the signal? Or does anyone have any other suggestions?
Do you really mean that you have the magnet on the crank arm and the speed sensor on the chainstay like it shows in the video?
If the issue is distance from the sensor to the display unit try replacing the batteries in both with brand new ones and see if there is any improvement. Weak batteries can cause wireless computers not to pick up the sensor.
I'm really having a hard time understanding why you would do this. It's kind of interesting that it can be done, but has no practical value. Are you planning to run 2 computers? One for speed/distance, the other for cadence?