Don't think you're going to be able to find anything plug and play. The WJ's I'm pretty sure have a PCI BUS, and the newer vehicles (that have the MyGig) run off of a CANBUS.
It would take quite a bit of reverse engineering to get the MyGig to be able to use the signals that the PCIBUS transmits.
I remember back a while ago when I had my 01 Intrepid R/T there were talks of PAC-AUDIO coming out with an adapter to be able to put the REC/MyGig in the LH line (which also uses the PCIBUS), but I don't think anything ever came of it.
I'm 99% sure the WJ has the PCIBUS, like they LH, because they only factory navigation option for both of them was either the RB1 or RB4.
This is what you would need, but they don't make it for the WJ