Officially, only account-type dimensions (Account, Flow, UD1-8, Origin, IC) are supported in the pre-aggregation property in all releases.
Unofficially, in most releases Entity also works, as you found out. I can't test it right now but I believe it works in 8.5 and above. We just don't make any guarantees about that being the case, today or in the future.
In the worst case, you can do it the "old school way", with a regular Formula on the Scenario.
(And when I say old-school, I don't mean no Tupac or Biggie - I mean Grandmaster Flash and the Furious Five...)
Thanks for the idea, Jack. Old Schoool. Nice! lol
