I would imagine that the traditional method of winching somebody aboard using the boom might not be practical on a beach cat.

However, if the person is incapacitated, the best way might be to "winch" him in directly over the side of the boat - a block and tackle hooked to the other side of the boat (opposite hiking strap or the such) with the length of the tackle NOT so long it that it extends over the rescue side, a tether from the end of the tackle over the side to a sling under the victims arms so he is facing away from the boat, then use the tackle to pull him up - the system would need enough mechanical advantage/purchase to compensate for the strength of the weakest crew member. You'll likely put a rope burn or two in the gel coat, but that's a small cost in a dire situation. A cleat on the block and tackle would be helpful or even necessary to hold the system in place while the crew prepares for the next pull.

If a person is not incapacitated, but can't easily get back on the boat, maybe something similar to the netting deployed in the side of ships could be used - add hand-hold loops to it maybe so you can get a hold where it is up against the hull. Made with the right line/construction, something like that could be stored easily onboard, deployed by one person, and give the victim valuable grips for hanging on to the boat (which would make it easier for the person on board to help) or getting back on.

Just some ideas...