I am guessing that if you throw a towel on top of the galley hatch for padding in case of contact, you can just let the gas springs open the hatch against the kayak. This would be higher than horizontal, plenty high enough for access.
Maybe if you rack the kayak on its side you could open the galley hatch enough. Shorter kayaks are no problem; we mount one of our Wood Ducks on the roof racks for display at show, with the galley hatch open all the way. But you’ll likely need to slack the aft tie-down strap on a 17-footer for full headroom under the open galley hatch.