IF you buy a JR RX like this one
http://www.horizonhobby.com/Products...rodID=JSP30600
which can have it's shift selected to either positive or negative you will be fine.
You can also plug your JR servos into a Futaba RX with no problem, in case you were unaware of that.
The manufacturers have made it pretty easy on us to do just about anything we want.