He is so cute! And you have apparently cracked the code - making a home that is so awesome that he doesn't want to leave is great!
Have you ever thought of making another play area for him? I am betting that a little ground squirrel would enjoy some tunnels. You could either get some large PVC pipe and fittings, or a little less expensive would be the corrugated flexible black plastic hose that you bury to drain water from your house. Like a giant hamster habitrail!
https://www.homedepot.com/p/4-in-x-1...0010/100212428
There is also a 6 inch version - you would ned to see which one will allow him easy access (they need to be able to turn around inside the tube).
If he is actually consuming 2 of the HHBs a day, his calcium intake is pretty much covered. If not, I would pick up a packet of the calcium carbonate powder that they sell at Henrys the next time you order. It is super fine and flavorless, which means you can sprinkle it on just about anything without him knowing. The Tums work well for emergency MBD treatment because they are so easy to locate, but I can't imagine that all of the artificial color and flavors in them are very healthy.