How about a clan preference option:
Search for a clan that prefers X number of matches.
Set a match preference for Y number of matches.
Again, a very nuanced potential feature that doesn't look like much, but if you are a clan leader, and you'd just like to make a 5:5 match, you are getting a full roster match pairing by default.
If you wanted a 5-member match, and could search that way, it would be a lot easier . . .. . .I think, probably.