A few thoughts.
Is the dry suit fabric water -retaining (eg wet suit type neoprene)? This can get quite cold once wet as the evaporation from wind can chill the contents (you) quite quickly. The membrane suits seem to be better this way. It might sound odd, but a loose oilskin worn over the drysuit would help. I've done this while scuba-diving and it actually helps a lot on the boat. Obviously, LJ on the very outside
The less silly looking way is as Chewy says, dress up underneath. You don't want to overheat when "working" so packing on fleeces is no help. Good gloves (sealskinz), mountaineering socks, neoprene neckwarmer, windproof hat, helmet. Wicking base layer is good - Helly make good stuff. A bikers neoprene kidney belt is worth looking at too - I find my lower back chilling and stiffening in these conditions.
Oh, and bring a thermos flask - that heat stays in the suit!