OK, I think i've got the solution: to put advice on AVMLockingService. I'm playing with lock and modifyLock methods as targets of my advisor. Still no results, but I think this is the way :-).
A question: is AVMLockingService really responsible for locking on AVM? I'm covering four methods with my advisor: lock, modifyLock, removeLock and removeLocks. remove* works fine - interceptor is called, but that's not happening in (supposed) case of lock and modifyLock.