Husse,

Although I'm not able to fly this manoevre, what I can suggest is that you try learning rolling circles on your sim, which is already quite difficult. A rolling loop requires lot of training and "trial-and-error" to be perfect, a sim is just what you need. Also, your model aircraft needs to be able to fly good knife edges, and have adequate power.

Now on to somebody who actually flies this manoevre...

Regards,
-Fabrizio