So sorry his belly does not feel good. You were right on track with rice and ground beef. I would boil up some more, make sure it is a long grain rice, not instant. The starch in the long grain rices are better. You can also use boneless, skinless, or ground chicken. Boil the meat and rice in a pan with extra water until tender. Sometimes it helps to give nothing by mouth for a little while, then start with a few tablespoons of the meat/rice mixture several times throughout the day as opposed to one larger bowl. You can keep him on this diet for a couple of days and when the stool is firm very slowly start incorporating a small amount of reg food at a time. 

It sounds like you did everything right, but if you rush back too quickly with the normal food it can start right back over again. Your vet may also prescribe Hills I/D prescription diet which is very similar to the home made version. I never understood why you had to get it through a vet, but it works well also. 

Good luck and hoping for happier tummies soon!

I totally agree. I never fast them that long. Just a couple hours for the gut to rest. The doc in charge will know best for Howard. Hopefully things slowed down for him ❤️