I just had to do this. I just sold my too small trailer and blocked up my boat. I tied the back of my boat to a tree, blocked all the way up to the hull (three cinder blocks), unhooked the winch, hooked up the trailer, and pulled the trailer out until the back fell onto the cinder blocks ($1.30 each from Home Depot). I moved forward a bit more, blocked the hull again in two spots and then pulled the rest of the trailer out, the rest of the boat fell onto the blocks and voila, boat is on the blocks, trailer is free. I had a few cinderblocks around, bought another 10 and put old rags on top of the blocks as not to scratch the hull, and it wasn't that hard to do. I had my father and neighbor stay on either side of the boat to make sure nothing went wrong, and it didn't as long as you go slow. I will post a pic later if I remember.