Putty would be my choice...
Just installed a Moen kitchen faucet (model 87666) on a sink with three holes. The escutcheon & gasket kit was used to cover each extra hole on either side of the faucet. Tightened down everything pretty well but I'm getting a leak through one of the extra holes underneath into the area below the sink. Is there a plug that I'm supposed to put in the extra holes? A web search for such an item shows some decorative covers that just snap in place, but also some that have a gasket and are tightened from underneath to make a seal. Moen just suggested to use some putty between the gasket and the sink which they never mentioned in the instructions... Should I use putty, or silicone?
Un-pipe and remove the faucet from the deck
Place the faucet on a firm table or the ground
repeatedly bash the faucet with a 22 ounce framing hammer until your frustration is satisfied.
Go buy a decent faucet.
Moen strikes again.
That type of plate is very difficult to seal because it does not have anchors through the empty holes. If you use putty, it may not comress properly and lift the plate off the sink when the center anchor is tightened. If you push it down, the putty could still push it back up, or not seal properly. A caulk, such as silicone or tub-tile caulk, will let the plate contact the sink without deforming it.
And when you want to replace it you will have to dynamite it off the sink
Which come to think of it, would be another good way of dealing with a Moen faucet, albeit a bit of overkill.
That would be the subject for a future question. "How do I remove a Moen faucet that was siliconed to the sink?" But in reality it would just be the mounting plate so maybe a new faucet would just slide through it.
I've always liked the look of horror on the homeowners face when I come in with sawzall in hand.