A great new paper showed up today, elucidating the gist of the subject mentioned above... the idea seems to be novel to me, so i thought it was more than worth being brought up to your attention :)
http://arxiv.org/abs/hepth/0311011
We show that the cosmological constant may be reduced by thermal production of membranes by the cosmological horizon, analogous to a particle “going over the top of the potential barrier”, rather than tunneling through it. The membranes are endowed with charge associated with the gauge invariance of an antisymmetric gauge potential. In this new process, the membrane collapses into a black hole, thus the net effect is to produce black holes out of the vacuum energy associated with the cosmological constant. We study here the corresponding Euclidean configurations (“thermalons”), and calculate the probability for the process in the leading semiclassical approximation.

I can't say much about it, since i quite frankly haven't even started reading the paper yet, but the prospects certainly seem auspicious! :)