Um, how far are we talking about lowering? I've usually had pretty good luck with either
A) Grabbing the free biner (not the one connected to the anchor/belay loop, but the other one that the rope runs around) and just pulling/redirecting it enough to allow rope to slip a little
B) If they can get off the rope for a moment taking the free biner (the one not connected to the anchor/belay loop) and just snapping it into my belay loop, so that it now acts in regular mode. (Though this really requires that you use it in Autoblock mode off your harness, which I often do.) (Remember, as it's loaded across the spine, whether or not it's open has no bearing on it's strength, so having it open for a moment while you connect it to your harness doesn't decrease it's strength. The only danger would be if you actually managed to get the rope out of the biner while you transition onto your harness, which would take an effort to do so and extreme stupidity to try.)
or
C) Make the wanker on the other end prusik a few feet.
If were talking about a non-responsive climber, a long lower (more than say 1/4 of the rope length), and/or a lard ass (whom you can't redirect the device and lower) the block and tackle with a munter will probably be necessary.