Comments? Well, sure:
1) You are to be commended for thinking outside the box.
I tried to do that -- I'm talking about boxes, not your TPMS mounting idea -- but eventually gave up.
- I bought an extra valve-stem from Max BMW, just so I could examine one up close and personal (without taking a stock one out, and thus deflating the tire). I thought maybe I could cut it down a bit, but that turned out, upon close examination, to be a lost cause (IMO). There's not much to cut down, and it also might entail cutting through part of the Schrader mechanism itself.
- I also bought a replacement for that, from one of the CarPlay device vendors, that alleged it was shorter, and so their TPMS sensors would work, front and rear (it was perhaps microscopically shorter, i.e., I feel they erred). We have one member here who went ahead and mounted one up front, but the clearances are too close for my liking, and they may change to be unacceptably close with new brake pads, or when some other factors come into play.
- I also thought about drilling a hole for a valve stem in the center of the rim, like every other moto manufacturer places it in their rims; I even talked to the service manager at Max about doing that, but they declined. I chickened out because there's a ridge there, a small angled-up area, so the wheel does not provide a nice flat area for a new valve stem to seal properly (at least the quality valve stems that I'm aware of). (By contrast, the wheels on my RE Meteor have a similar ridge, but by the valve stems that changes to a small plateau, a mesa-like area, just to obviate that issue. BTW, during my last tire change, I had the local RE shop replace the stock rubber valve stems with nice offset metal ones, for both easier access and because I got some TPMS sensors, kind of like you, included with the cheap CarPlay device I bought.)
2) I think the signal from an external-intended sensor mounted inside a rim may not make it reliably through the metal of the wheel -- when the wheel is antipodal to the receiver -- and may not make it reliably even when sort of in-line with the receiver, because of just the tire's being in the way (because of the thickness of the rubber, which also may have embedded steel cords).
I base this possibility on the occasional issues I've had over the years with a FOBO sensor on the rear of a couple of bikes (including the C 400 GT, before I spent all that money to get the internal BMW sensors installed). That is, sometimes -- not all the time, but sometimes -- doing a pre-ride check with the FOBO(s), I've had to rotate the rear tire (with the bike not started, still on the centerstand in the garage), because the sensor was not giving a readout. This was presumably because the sensor was positioned such that it had to go through a lot of metal, or plastic, or something, to reach me (standing up) and my phone.
3) I think it would be a real pain to have to replace the battery in an external sensor that had been mounted inside the tire.
That is, the batteries in internal sensors seem to last
years longer than those in external sensors. If you go through tires at least once a year, maybe this wouldn't be an issue.
You have your own tire-mounting equipment?
4) That would have to be some very strong, very long-lasting, very high-quality, glue.
The outward force (I don't want to get in a centrifugal vs. centripetal discussion) would be constantly trying to throw the sensor off the rim. And perhaps through, or at least damaging the tire. Or maybe just rattling around, making handling weird.
In any case, it's not something I would risk, but that's me. If something's inside the rim, I would want it bolted in place, as the BMW internal sensors are.
5) If you think you might go through with your plan, I would test it out, perhaps by duct-taping one in place inside the front wheel; then go for a short ride, and see if you get a reading from it.
Or you might even be able to check it without actually riding anywhere. I bought this wheel-rotating stand --
https://www.harborfreight.com/motorcycle-wheel-cleaning-stand-98800.html -- from Harbor Freight specifically so I could rotate the front tire easily, in the early days, when I was examining what would happen to an external sensor mounted up front. (It turns out that the stand comes in handy the once a year or so when I clean the front rim.)
If I understood your proposed scenario correctly, those are the thoughts that come to my mind, offhand. Good luck.
