There's one solution, it has a few parts, and your not going to like it.

1. Mandatory unlock. Either lock alliance roulette at completion of an expansion until the raids are unlocked, or automatically unlock all raids at that point (but don't complete the quests, let folks do the quests when they want them, latter).
2. Mandatory Ilvl. Alliance roulette has to require the ilvl of the highest dungeon possible at all times.

Without both it'll still be possible to force folks into crystal tower.

Why care? Because every time somebody forces crystal tower, that's one or two parties of people that might be doing what alliance roulette was meant for, to get people unstuck who need to do alliance raids. Without people doing the cheese, crystal tower raids will show up more often due to there just being more players at that level range, and that's okay, it'll at least not be 8 to 12 hours in que waiting for a raid to happen in PF. I've seen coils go faster in PF.