SUMMARY: He did it!
Thinking about it last night while brushing my teeth (yes, a great time to be creative), I knew that Chip was already doing everything that he needed to do to get through the door except that initial tiny push. And it occurred to me: As long as I'm doing that for him over and over, he has no reason to do it himself.
So, Operation Doggie Door Tough Love.
This morning, after I let the dogs out and set up the dog door, that was it. If he wanted to come in, he'd have to do it himself.
At 7:15, when Boost and I stepped out the front door for her to get the paper, I heard the flap open and shut lightly, and sure enough, Chip was standing there. But then he just stared at me through the sliding door. I knew that I was on the right track.
I tried to make it worthwhile for him to come through.Made sure both dogs were inside with me. I gave them treats and praise and used the clicker when he was watching. I played tug and fetch with Boost while he was watching. He'd watch a bit, sometimes just barely shove the door, and then go off into the yard again. I missed photos of his first 3 or 4 attempts, but then I was ready.
8:05 - Quick poke and turned away
8:12 - Poked nose in and wandered off again
8:18 - Looked at it for a bit, poked at it a couple of times, then left again
8:26:59 - He decided that this was the time to do it!
8:27:27 - Ta-da!
Now--will he do it again?