Sounds like hauling a boat up the slip that way..could be a waiting for an accident to happen.
When I was in the same situation with my heavy harshell boat.. I fixed an electric winch to the trailer drawbar. The winch was on a plate that I just slotted over a couple of pins welded to the trailer. Very easy to attach or remove.
Attach the end of the winch to where you are thinking of attaching the pulley.. winch to there and chock off the trailer wheels so it cant run backwards. Re attach to your car towbar and winch to there..hook up and drive off safely.
Alway keep a chock at hand ..so if you think something is not going right..you can chock of the front jockey wheel ..instantly. I even replaced the wire with a winch tape as I didnt like to think what would happen if the wire broke.