@PaulDuffy, sorry for the delay in responding. I saw this some days ago, then ment off my list.
I had the exact same query some months ago (you can see below)
Short answer, is you could not. As far as I can still work out you can not.
However running some logic, you should be able to get it to work.
For me, I never did, this was primarily due to some things working sometimes and not others, which ment Harmony Activities would fire even though power wasn’t on.
What I did in the end was, a single activity to turn power on. Once on then I did another activity for the Entertainment set up you sought.
If you come up with a working set up, please let me know.