To some extent this is true... not all 12 million would deport themselves.
But asset forfeiture would definitely make a smaller haystack, and provide less incentive for newcomers. Also, guest worker programs would become far more attractive.
And the INS would have a profit motive to enforce the law, though it's sad that's necessary.
Actually, the way you want to use this appeals to me. As your statement is accurate, paying assets siezed as commissions to the INS and Border Patrol agents directly would motivate them to enforce the law regardless of the recalcitrance of their superiors. You've got something here.
ijcr and others suggestions about employers have merit also, but your point about existing law is the place to start to sort out who is a "knowing" illegal employer.
I enjoy reading your opinions, go ahead and submit some to likely venues, I think you will be pleasntly surprised.