Does the jib halyard
lead back to a winch
or cleat in the cockpit? If not you will still need to go to the mast to release the halyard.
I would not say through bolting is overkill so you might get away with screwing in the fairleads but do take careful note of the cautions from delmarrey about getting water
into the deck core through the screw holes. You do not want a wet core.
The main question will be how much load will be on the fairleads. If the downhaul line goes straight through the fairleads without pulling up or sideways at all then you can probably get away with screws.
Also, you will have to have something bolted securely at the bow where the downhaul comes down along the forestay and makes the turn to go back through your fairleads to the cockpit. Screws will not work there but you may be able to find a spot around the bow where you can attach a block without adding a new fitting.