LADIES AND GENTLEMEN, WE HAVE ACHIEVED DOG SWEATER!
It's a quick, simple design, it's warm, and most importantly, it's pain-free to get him into. You can't see it well from the picture, but there's a button right behind his leg. The sweater is worked top-down seamlessly and knit in the round until the shoulders, where it splits into a cape-like top piece and a narrower belly piece.
To illustrate, here's what the cape part looked like pre-buttons:
Getting it on him goes like this:
Step 1: Pull sweater over dog's head.
Step 2: (Optional) Watch dog frolic about like an idiot doing his "I has a sweater!" dance.
Step 3: Button the corners of the flaps to each other, closing the body of the sweater.
No fuss, warm dog. It's a really easy design to modify and add to, so I'm planning on doing a few versions of it for Hobbes for this winter - including at least one with sleeves.
I'll whip up a pattern when I get the time.