First, let me echo what others have said -- if you are properly weighted/balanced you should not drop like a stone when you take off your bc. You can make yourself more comfortable by shifting some weight from your harness to your BC (or BP/W for that matter). All sorts of ways to do that (BC trim pockets, cam weights, ankle weights around the neck of the tank valve, use a stainless vs. al backplate, etc, etc.)
Second, if you are diving dry, you could simply add a bit more air to the suit before you take of the weights.
Third, you could board the boat with all of your gear on (unless it is not allowed by the charter company).
Fourth, as TS&M noted you could pull the rip cord on one or both sides. You could also fish a weight or two out the top of the pocket (mine has velcro there).
Fifth, Thalassamania offers another idea -- essentially clipping off your harness.
FWIW, I own and enjoy the DUI classic -- for me, it is way better than a weight belt!