Round-robin playoff competition?

[Dicky Leonard]

Hey all, I've been banging my head against a wall trying to figure something out and am hoping the folks here have some insights.  I'm trying to create a league structure where promotion and relegation playoffs do not use the knockout format, but instead are conducted like a normal round-robin league (i.e. every team plays each other team once or twice).

 

For context, I'm doing this in a pyramid that I'm building where a large number of semi-pro and amateur leagues would compete for a small number of promotion spots into the professional section of the pyramid.  So it's really like those teams would play in a local league to qualify for a spot in a second league from which they could gain promotion all in the same season.

 

Hope I'm not missing anything obvious here...