Hi,
You can use a 'Y' reverser where one channel is reversed only, or run a standard Y with a reverser after. These are OK, but you will find that the reversed servo, will after some time not return to its central position, as the reversers tend to 'drift'. I have used these in the past, and have got frustrated with their operation.

The best way to do this (exept for buying new radio gear), is to use a JR matchbox. I swapped to these after having problems with the inline reversers.

The match box allows you to control upto 4 servos from a single input channel, then reverse any of them by programming it, which is very very easy.

Hope that helps.

Regards

W