I'm no expert but, it seems unlikely a monti would overtake a hammer. Monti's could certainly shade them out from above but, side by side, I would expect a hammer to sting the monti into submission. Having said that, if it is a monti and is indeed attached and overtaking a hammer, I would gently wave my hand (or something else) over/around hammer to get it to retract and then break off monti with fingers/tweezers/tongs. If you take this approach, I would be sure to get the whole thing. You wouldn't want to have to go back at it multiple times. However, as mentioned initially, it seems unlikely that a monti frag that falls into a hammer is a threat to the hammer.
Matt