I'm using a Time Capsule to do Backups, I've been doing this for a while now. The problem is that the backup begins small and with time it becomes huge. So restricting its size would make Time Machine use it's own space saving operations (I guess).
My idea would be to change the sparsebundle's size limit to a size much smaller than the hard drive's size. Since the sparsebundle is where the backups are done it should restrict available space and cause pruning when that limit is reached.
Would resizing the Sparsebundle cause any problem for the reliability or function of Time Machine?