"Controlled group" and coverage (dis-)aggregation

[AlbanyConsultant]

I've got a controlled group (technically a group under common control, since at least one of the entities is a partnership) where the same four individuals each own 25% of each entity H, G, and S. H and G each have their own plans, which are mirrors of each other (deferrals only), while poor S has no plan at all.

Luckily, S is a staffing company that provides per diem employees to H and G, and both H's and G's documents specifically exclude per diem employees, so the vast majority of S's employees are not eligible by class, and since most work less than 1,000 hours, they would never meet the statutory guildelines and therefore don't impact the coverage testing. I know there are issues with long-term employees from S possibly being considered employees of H/G after a year, but that's a question for another thread (though it may be coming soon!).

From reading Tom Poje's responses in this thread:

http://benefitslink.com/boards/index.php?showtopic=29893&hl=

it sounds like I have to make the same aggregate/disaggregate election for both coverage (410(b)) and 401(k) testing, but am free to select either option. Have I got it right? Are there any circumstances that would force my hand one way or the other (besides, of course, that doing it one way fails and the other passes!)?

This is my first time dealing with something of this complexity, so if I'm overlooking anything else, please feel free to let me know.