You can squish some butyl tape around where the leaks are. This can be removed very easily later. I did this around a hatch and a winch that were leaking, and they stayed dry until I rebedded them. You'll want to put it around the entire hatch, not just where the leak seems to be, since water will wander a long way from the source.
Whatever you do, don't block the leak from the inside. You want the water to drip, not work its way into the core or other structural components.
On my boat, there once was a leak from one of the light fixtures. Some previous owner just used caulk around the wires to stop the leak from dripping. The only way I discovered this was by removing the headliner, all looked dry when the light was removed, except for the odd location for caulk. Under the headliner was a wood backing that was rotten and had to be replaced. Yuck. It would have been a better idea to find the source of the leak and repair it! All fixed now...
Check out this link from Maine Sail on how to seal deck penetrations: Sealing the deck