Not an Android Developer here. Is there no "pauseForGC" function in Java/Android? I know AS3 has it, and you can use it to suggest GC at a point where there aren't any animation going on.
There is a System.gc() call which is essentially what you described, but it doesn't help with allocations freezing the UI for memory intensive applications
You can use the System class to do this. "System.gc()" will request a GC run. Of course, its only a request. There's no guarantee when, and if the GC will fulfill that request.