I've read the posts over on the Hydraraptor blog about using a toothbrush head and a knife to clean up the expanding extruder material. nophead's now partially melting his toothbrush, and it still requires you to trek halfway across the machine to clean up. Not a concern when you only do it once or twice a part, but I can see issues if you need to clean up when doing discontinuous extruding.
Here's what I'm hoping to try when I get a chance. Take a very small motor or 180 degree rotary solenoid. Affix a bracket to the shaft with a 45 degree bend. You're probably going to want something that has useable properties in your extruder temperature band for this. Affix a thin (and possibly sharp!) piece of metal to this bracket. Affix this whole contraption on a bracket near your extruder nozzle at 45 degrees. The idea here is that when activated, the solenoid moves the blade from 90 degrees parallel to immediately underneath the nozzle. Control or spring return would reset the system when de-energized. This severs your material and can also act as a block to partially prevent drippy nose syndrome.
Blades extracted from a disposable razor would probably be just right. You'd want it sharp and wide enough to block the nozzle but not so wide as to be unweidly, and thin to reduce plastic displacement and to allow you to trigger the cutoff near the piece, thereby reducing stringing. Very useful for between layers or when non-continuously infilling. The major disadvantage is that you have something ELSE hanging off the extruder now. The blade and motor assembly, when in storage, at least can be made to normally rest above the work zone.
Anyone else have an idea on this?