This isn't in the law. It's in the administrative code, in a section that I had not previously bothered looking at.
TITLE 37, PART 1, CHAPTER 6, SUBCHAPTER G, RULE §6.83:
For most other states that issue non-resident permits, the applicant does not need to set foot in the state.(a) All classroom and range instruction for license applicants shall be conducted in this state.
Also, since the application, photographs, fingerprint cards, etc., must be delivered physically to DPS in Austin, teaching courses on the moon is even more impractical than I thought when I jokingly suggested it.
Unless Texas annexes the moon.
Thanks, WildBill, for bringing this point to my attention.
- Jim