one way to do it is to tie the trap wires to the outer end of the crossbars, connect the front stay to a stick to the base of the mast. (could use the hiking stick) and connect the winch line to the forestay (at the top of the stick) you may need to tie a line from each trap end to the top of the stick also to keep it from falling over.
The way I would do it on a H16 is I would put both side stays at the top of the chain plate. lower the front of the trailer to the ground then get on the tramp and toss it in place. let gravity hold it there while you attach the forestay. you can also use the wind (from behind the boat) to hold it up. But you must have good steady wind (that is why you are putting up the mast right).