A vast majority of the dual dashmisers I have seen are self-contained and had only one pattern. I have seen one or two that had selectable patterns with the internal supply, but I consider those rare. Making the unit a remote dual head strobe would work, but then there is the issue of more cabling to install.
Or, you can do what I did, I took the strobes out of my dual dashmiser and installed the Whelen 600 Series Linear Super Split LEDs. All you need is power and a ground, and you have the option to bring the sync wire out as well. TIR6s work as well. I converted a friends dual dashmiser to TIR6 heads and it looks pretty good.