There was a post on Agon some time ago talking about a blue putty. Bluetack - I think it was called, some members had used it for securing speakers to stands. Help me out here someone.
At any rate, I bought some on-line for $7-8 and used it on my HT setup. Man, it grabs the speaker and wont let go very easy. About two months ago I upgraded speakers. It took 10-15 minutes, but I separated the speakers and the stands and got all the old putty cleaned up. Not a mark on the speaker. I stuck 5-6 pieces on the new speakers and ... well, there you go.
Works like a charm - and no damage to the speakers. Some of the people who posted even used it for securing heavy power cords to the power sockets on their amplifiers to keep them from falling out.