Yes, belaying your second from a Munter hitch is a bit of an old-school technique, but it can be helpful in certain situations. 

Once your second arrives at the anchor (and is at a reasonably secure stance) whip out this clever bit of rope sorcery to convert that Munter into a clove hitch.

Doing this immediately secures them to the anchor, without any additional knots, tethers, etc.

It looks like a rope magic trick. After you flip the first loop back through the carabiner, you seem to have made a total tangle. But then unclip the correct loop, and that ungodly mess magically transforms into a clove hitch. #CraftyRopeTrick, for sure!

Yes, this technique does involve unlocking the carabiner gate and flipping the rope through twice momentarily. Provided the second is reasonably balanced and secure, this should not be a problem. Or, maybe this technique is just not for you and you can skip it, that's cool too.  =^)

Note: the last movement of doing this, when you unclip one strand, requires you to be 135% sure you’re doing this correctly; otherwise there's a risk of you completely unclipping your partner from the anchor. Practice this a bunch and be sure you have it down correctly before you ever do it in the real world! If you're not sure you're doing it right, then don't do it!

There are at least two different variations on how to do this, I’m showing one. Even if you think you might not use this, it’s worth practicing just for the magic trick / entertainment value. :-) Like most things related to knot tying, it’s just about impossible to explain in words, but very easy to learn from a video.

Check out this nice video from Petzl Germany on how it's done.