I can do a decent 1 roll circle and the trick for me was 1st of all just a ton of practice.

Other than that its making the rudder transition on the backside from left to right (or vice versa) was the harderst part.

Hrees how I do it. Say you are standing at the 6 oclock position.
Doing an outside roller counterclockwise.
Start the plane by very sowly rolling continuously right, feeding in down elevator and left rudder to start the turn. The plane should hit knife edge at the 3 oclock. As the plane passes through knife edge at about 2 oclock I start to apply right rudder and down elevator increasing the right rudder until Im almost full right rudder at the 12 oclock position. Continue to hold right rudder and make the turn but at about 10 oclock as you are coming out of inverted approaching knife edge start transitioning from down elevator to up elevator to continue to steer the turn. Now you are back on knife edge and at the 9 oclock position. As you make the last quarter you will transition back to upright making the last quarter with left rudder back to where you started.

It sounds easy and it is once you have it down pat. BUT, Getting there for me took about 1000 tries on the simulator. The 1st time I tried it with my real plane I did it, but it took a lot of practice to make it flat and round. Its still got some work to get it just right. [8D]