Maybe I am missing the main point. If some teams are pre-bowling, unless they pre-bowl against the actual team they are bowling against for that league session, how can you consolidate? I couldn't imagine trying to push a league down one or two pairs by trying to move teams around as league is starting up. The logistics involved are a bit too much to try and accomplish consistently.
Just to make sure I understand, are you saying for a 20 team league (lanes 1-20), lanes 9 and 13 have teams that have pre-bowled, you want to put the teams on 10 and 14 together and move the entire league down one pair to give you more room for open play? Would be wonderful, but I wouldn't have done this in my time managing. A lot of times the manager on duty may or may not know about the pre-bowling teams and wouldn't realize the issue until the time practice starts. Once you get within 15 minutes of practice starting, you can't start having half the league or more move just to give you another pair for open play. I see too much complaining coming from this.
If it becomes an issue with certain teams continually pre-bowling just so they can have their Friday's off, well, I bet that would be the only year they bowl on that night. Many people don't realize how a Friday night league affects their weekends until they do it. And if they start missing because of the affect it has, my bet is they won't do it again.
I am not a pro-bowler, but I do play one on BallReviews.com