I have always used the right stick for the rudder on 3-channel planes that don't use ailerons. The roll that results from rudder use is so similar to ailerons that you can just pretend that the plane has ailerons while flying. You can even do a roll by just using the rudder. If your radio features mixing, you can mix the left stick to the aileron channel so that both sticks work the rudder, this lets you practice using the left stick for the rudder while still having the right stick controlling the rudder.

The rudder on 4 channel planes.....it's not just for taxiing!!! Learn to use it!!