Complete tax amnesty for 3 months. Now, it has to be kept simple. The taxpayer is responsible for documentation. The government will not spend a lot of time with a goofy "application" and "approval" process. (We saw how well that worked for the mortgage mess.) Once the debt is verified, payment is made by the taxpayer right there. No further penalty or process involved.
Didn't file with the IRS a couple years ago? Get that return together, pay the amount you would have owed back then, and send it in and be done. No interest. No penalty. (No refund back to you either though and to get amnesty and stop the IRS process, you must file return[s] for the missing year[s]).
Behind in personal property tax on your car? Find out how much and pay that amount only. No interest. No penalty. No problem.
Property taxes behind? Same thing. Pay it in full, without penalty or interest. No more threats of a tax sale of your property on the steps of the courthouse.
I think this would work. But it has to be kept simple, to keep administrative costs to a minimum. Simple works here. People would take advantage, knowing it would clear things up for good with the taxing agencies. I think the money would roll in.