Received a reply from K9 safety. They did not see a way around the Mercedes-Benz transponder on the www either, but are checking.
Also received a reply from this place: http://www.smartkeystarter.com/
They have a video showing remote start of a Sprinter, but seem to still be in development.
I keep remembering how nice it was to look out the window and remotely start that Jeep sitting buried in the snow, but at least I think I solved the keeping-stuff-from-freezing-while-parked-for-a-week-in-the-bitter-cold for less than $30.