I know that Dakota Digital makes a signal splitter and that's what I was going to use, but if it was possible to do it with your controller -- I would get rid of one more complication. Here is the Dakota Digital Universal Speedometer Signal Interface:

Dakota Digital Speedo Interface

If someone is going to be using the 46RE transmission, there is the problem of just the output from the transmission being an electronic signal. Those that use the stock speedometer cable setup will kind of be screwed, but there are workarounds (i.e. cable generators or changing to a GPS speedo). Those of us that will be using electronic speedometers will be all set -- I was just trying to get the electronic box count down in my car.

Mark