I wonder if bukkit is powerful enough to do this. Make a slime stick blocks together exactly like sticky pistons. So if one was to put a sticky piston under 2 cobble that were 'stuck' together and extend that piston, when it retracts it would pull both blocks down again instead of leaving the top on floating in mid air... Don't think bukkit can do this but worth thinking about. Right click with slime lays a sticky piston slime thing using the same mechanics as placing red stone wire. This would also enable you to build roofs on houses out of sand cause sticking the block to the one beside it would stop it from falling.