your idea was also floated as a suggestion to the BB gods a few months back. D-league style Private league's, where you could train extra players. got a bit messy and its a big feature that i dont think the BB-developers wanted to implement ahead of other features.
You do know of course though, that Private League games do not contribute to player development? Only league and scrimmage games contribute to training and experience. (its just the way it is in the game).... If you organised it as scrimmages, you would have to make sure users booked their scrimmages against the correct opposition each week. In saying this, some users do this between other users already, so maybe u just need to find a couple of guys in ur league to constantly book scrimages with? or even another league in Div IV? different teams, mix it up a bit.
Brett from ACT Blaze organised a Private league earlier this year, where basically we gathered teams who had salary of roughly $350k - $450k such that we could try out different tactics against similar competition. Its worked quite well, i have found value in it, although teams will buy players for their own league purposes and of course, its impossible to enforce strict rules in a Private league scenario. so of course, suddenly one team has a salary of $600k and it becomes a bit uncompetitive, but ive still found the value.
But as a suggestion, you could make a Private league, where you have a gentlemens agreement such that teams could only be made up of players under a salary of $10k i think you may gather some interest from teams in Div III and IV. See how much interest you can gather up in the forums, go to each league forum and message them there. You'd only need 8 teams including urself to make it worthwhile.
and also, welcome another West aussie! im from Perth as well. Tried out at wanneroo wolves back when i was a 16 year old, but never made it very far. good old SBL. its much better now than back then.