The idle speed is controlled by the ecm - in your case I believe its the ECM-08 CANBus version.
The dealer could do it but likely won't as the factory doesn't want that type of change made...you can ask and see what they are willing to do.
The diacom software package has the ability to reflash the ECM but their literature isn't clear if there's anything 'extra' required to enable it....suggest contacting Rinda directly as 'ask before you buy'. Worst case, there are many aftermarket 'reflshing shops' that could satisfy your need.
The factory offers a digital sync package but, as far as I know, it will only keep both engines at the same RPM - using only the master throttle. Won't help for keeping a constant speed over the ground without operator intervention when the environment changes...