Almost there. Got MixMeister to calculate the BPM (there's an earlier freeware version out there) and the created the Virtual tag:
.BPM = $If(<BPM><100,0$Left(<BPM>,1),$Left(<BPM>,2))0 (the leading 0 allows proper sorting)
But... tried restricting Auto-DJ to ".BPM is [playing track]", to no avail. What gives?
Obviously a cooler version would be an Auto-DJ checkbox that weighs in the BPM of the songs when choosing similar artists/tracks, the same way the user can already do with genres.