Oh yeah, I should've mentioned fretting the lower strings for a unison (1:1) to the higher adjacent open string. No beating in this unison yields equal temperament, due to frets scaled accordingly, so it avoids the problem I mentioned... but introduces likelihood of intonation issues (or simply bending the pitch) as you say.

I had been thinking about listening for beating in the 5:4 and 4:3 intervals using open strings, which does present the just temperament problem, and harmonics on open strings to make a unison unfortunately shares this problem 100%.