Actually, you can move in a grapple, just not as freely as normal. It's still enough to use any other maneuver in the book while grappling, as there is no text saying you can't use maneuvers in a grapple. In fact, the supernatural ones automatically can be used, without question, just by being supernatural (a dragon can use its breath weapon while grappled, for another example). I, for one, refuse to believe the extraordinary maneuvers are
more restrictive than the Su ones.
As for grappling, the text says "...select one spell, effect, or other
condition currently affecting you..."
So...I decided to check out the handy 'ol "condition summary," and...what do you know? "Grappling" is on there.
http://www.d20srd.org/indexes/conditions.htm
Now, I can think of reasons I wouldn't want to allow it as a DM, but it seems fine by RAW. And really, the custserv already said you can shout down an AMF, is it really so extreme that it also ungrapples you?