Well for starters, soaking is going to be your best bet for removing the rest of the stuck shed. Put your snake in a tub with luke warm water, no higher than mid body height of the snake. Also, make sure you put a wash cloth or something along those lines in the tub, so your snake has something to rub up against to get the rest of the shed off. Soak for about an hour tops, and you should be golden! If there's still some stuck shed after the soak, let him run through the wash cloth while you hold it with slight pressure to help get the rest of the skin off.

Can you elaborate a tad more on the "swimming motion?" Only thing I can think of, is that he's just stressed and is trying to get away.