So I'm doomed to have my Check Engine light go off at least once a year.

Does that sound like a reasonable series of assumptions?

Yes it does. Welcome to the wonderful world of OBD II. We see a large rash of the same problem in the beginning of the summer.

If so, does anyone know if the tank pressure sensor can be defeated, and if so, would there be any other harmful effects of doing so (other than its inability to detect a real leak if one happens)?

Aside from the possibility of it being illegal (probably is, don't know for sure), you'll be screwed warranty wise if your emissions fails. Not sure if it will hurt anything mechanically.