(thanks to mdules13)
The best loophole is still that you can sign prospects to an ML contract, then immediately take them off the 40-man roster without passing them through waivers. It gives you an edge in negotiations and costs nothing but an option year.
(thanks to ruffleswest)
Put as much $$$ into both College and High School as you can each year and then max out your Advanced Scouting budget. I seem to end up drafting around 22 - 32 spots with most of my other teams that I have had for a long time...you can always end up getting a top 10 player (or better) that far down if you put the $$$ into it. Of course this stategy won't work if you don't care about the amatuer draft or projected ratings and have a high salaried team who spends all their money on overpriced F/A's.