This is going to sound super hokey, but been doing it like this for twenty years...
Find a place you can set the boat down for a while...preferrably near a tree or a phone pole to tie off with, get a floor jack and some large towels and blocks of wood. tie off the rear of the boat with your tow vehicle still attached, undo all the tie downs, take a little weight off the trailer with the floor jack under the boat with some blocks of wood and a fluffy towel, pull the trailer forward and keep moving the floor jack so not to hit the trailer then set it on some tires or if you have them hay bails with towels on them (works bitchen), keep pulling until the boat is of the trailer.
To put it back on, get a Come-a-long and spray the bunks down with soap and water and disconnect the trailer from the tow vehicle and pull it back on, works slicker than owl shit...
We did this with an Advantage 27' Victory (brand new, $67,000) inside the Cow Palace boat show in about 15 min.
