I appreciate the help, and am glad there are only 2 answers. Could've easily turned into a 3-page discussion.

After 10 years in the business, you'd think I'd know the answer, but it's a situation I'd never come across and didn't want to waste time troubleshooting after the fact. I went with the diode solution since I happened to have some (I'd done it before using 3 separate wallwarts to trigger a single power controller so it made sense). Worked first try, which is always the goal.

Impaqt & Warren, thanks much.