I've run into several cases where I've needed to perform a revolved cut on a part which has no plane on which to sketch.  I've been successful in creating a plane which bisects the part and can sketch on the plane, but I can not reference any part of the bisected part, so it is difficult to accurately create the profile to be revolved.  For example, if I have the following part:

and I want to put an irregular groove in the top surface.  I'd like to do this by creating the profile of the groove on a plane that bisects the part and then revolving in around the central axis.  Is this possible?  Again, I can get the plane, but I can't reference any of the geometry in the existing part.

Thanks,