When I played in a box league, that worked fairly well. Having to play a set number of matches in a set period meant most people got involved... even if most of the matches were in the last two weeks. The ones that didn't - well, they just got relegated or kicked out. The head coach switched it to a ladder as it meant less (i.e. nil) administration for him, and it's just stagnant.
I'm tempted to attempt an unofficial mini league, possibly with an entry fee just to keep people interested. Any monies collected would be re-distributed as prize money. Maybe after Christmas.
My String Journey: http://tt.tennis-warehouse.com/showthread.php?t=362403