I've seen it used--works just fine. JR must be the master, and futaba must be the slave. That's how you'd do it anyway. I can't remember how the power issue is resolved--but I don't think the JR is capable of supplying power to the futaba. The instructions will resolve that issue for you.

Definitely the route I'd go, unless you want to buy your own buddy box (which isn't a bad thing either).