I have noticed ladders as I've been looking for a boat and tried to figure this out as well. My dogs never had a problem in the cuddy.
At Lowes or Home Depot there are hooks to fit ladders. I though of taking plywood
and screwing two on a small platform to form a longer step. You tilt it up to hook it on the risers and it locks down just putting it on. I looked at one boat and thout 3 larger steps would do it. After use, lift
up, it slides off and store behind the ladder.
I think these dohickeys are in the paint
department. You could make the bottom brace from wood with a couple small blocks screwed on at the angle needed for the ladder. It just uses the risers of the ladder makeing detachable steps.