The reason you would want to mix roll and pitch control is to counter adverse yaw from the down aileron. Since you are flying a 3-channel airplane which uses rudder causing roll-due-to-yaw as roll control, you have no need for this type of coordination.

If you are just speaking of using up elevator to hold altitude in the turn, you would only use it after neutralizing the rudder. If you try to apply elevator as you roll in, you will probably climb. During roll in, unless you are making a very slow roll in, you only need a very little, if any, elevator.

If your plane has room, I would suggest you add the 4th servo and connect it to your nose wheel steering and the rudder channel. Your rudder is in the aileron/roll channel. This way, you can learn to steer on the ground with your left hand. You'll need this for your next plane.