I promised myself I would post what worked for me, so here it is.
Heat patches. The ones manufactured by Deep Heat for joint and muscle pain. Just slap a patch on the abscess and let it heat up your butt for 8 hours. It's like a warm compress that retains heat for much, much longer than a hot cloth does. It burst mine within a few hours.
Heat increases blood flow to the area, turns off the local pain signals, brings the boil to the surface, and softens the skin, all of which makes it more likely to rupture.