I figured out how to get Jasper to eat Critical Care.
The 1 ml medicine syringe is too small to draw in the mixed Critical Care, but the larger feeding syringe can. I can't use the larger feeding syringe to feed him, because it's nozzle can't get past his molars, which is the only way to get him to swallow syringe fed food.
However, the nozzle of the large food syringe is exactly the right size to fill the smaller syringe from the back end.
I mix up some Critical Care, and fill the large feeding syringe. I then pull the plunger out of the small medicine syringe, fill it, replace the plunger and feed him. The syringe can't suction up the Critical Care, but it can expel it. It's slow and annoying, but it works. I used this trick to get about 18 to 20cc of Critical Care into him this morning. This is in addition to 8cc of banana baby food My Wife helped me give him.
While he still isn't eating pellets, he is eating lettuce, carrot slices, sugar snap peas and a little broccoli. He's also been seen chewing at least a little hay.
The family who adopted Tatum and Winona gave My Wife and I a gift basket that included some Oxbow Vitamin C treats. These have a bit of sugar, so I can't give them to our own bunnies, (Most of whom need to lose a few ounces) but Jasper eats them like candy. I mixed some in with his pellets and scattered some among his greens. At the very least, he'll snuffle among his pellets to get the treats.
All told, he's up to 4 pounds, 8 ounces. This is the weight he was at when he came to us, and is up and ounce from where he was yesterday. His droppings have even gotten larger.
He gets dropped off at the vet's office tomorrow. If all goes well, Tuesday night he'll have freshly trimmed teeth!
Thank you for all the well wishes and advice. A number of the tips I've been given have proven useful. Now if only I could find which box our food processor is packed in...