Sort of. You can do it all inside Mocha. You only need one track - make it a spline that goes around the ring with enough room to add a soft edge and set the value of the soft edge.
Make a cleanplate using preferably your first frame. Click the Align Surface tool (the square at the top with the diagonal arrows pointing out) That way, your cleanplate fills the entire frame, not just the area of the default surface tool. Use that image as your insert source and set the mask of the insert to the spline that you drew.
I find this method easier for the type of “remove” you’re trying to do. Drawback is that it doesn’t to the lighting adjustments that the remove module is capable of.
Full Disclosure. I’ve only been using Mocha for a few months and I teach a motion graphics and animation course at a University. At times I find it fun to try to answer these forum questions. I take no responsibility for the accuracy of my advice and do not speak on behalf of the amazing Mocha Team, BorisFX or its subsidiaries.