I have not seen a wiring diagram for a 2006 yet, but there may be a pink wire listed from the ignition module that is a tach output. If there is, I believe it has a combined signal for a dual fire tach.
Also Crane makes a tach adapter but it was intended for an aftermarket single fire conversion on an EVO. Can't say for sure that it will work but you could give it a try. It won't be plug and play and would require connections to the coil plug.