I couldn't find someone who knew how or could do it, BUT I found another dealer that happened to have some new Load 60s with precisely the specs I was looking for, so that's the route I took. I'm not confident there is a way to do this - at least I could find no information about it. Clearly it has to be possible because there isn't something fundamentally different about the bike - it has to be just different wiring or something of that nature, but there isn't info on it, which makes it a bit of a no-go, at least in the Seattle area.
Regardless, I'm super happy with my Load 60.