That's similar to what we did. The gap we made was a "corridor" composed of a folded cardboard box and the curtains by the double sliding door (we've learned from experience that, without a tunnel to guide them, squirrels will counterintuitively flee into the living room as opposed to making for the sliding glass doors). We even put peanuts in the corridor. The squirrel didn't take the bait immediately, so we left the "tunnel" in place while the heat leaked out of the house. We closed it back up again after a couple of hours. Hopefully he's gone. Haven't heard a peep so far.