This whole "felons voting" thing is sort of bogus. You make it sound like inmates are finding a way to vote. In the State of MN, once you have been released from jail. Finished probation, and otherwise "paid your debt to society", you have to go in front of a judge and ask for your voting rights to be restored. Many people are unaware of this. If YOU got out of jail and did your time and were a normal citizen, wouldn't you just assume you would be able to vote? This whole schedule a court date, possibly hire a lawyer, and "restore your voting rights" thing isn't well known, and many people who have been out of jail FOR YEARS, do what every American is supposed to do and show up at the polls and cast a ballot. There is legislation under review to automatically restore voting rights upon completion of your sentence - which is much more reasonable. A fundamental right, like voting, shouldn't be held behind lock and key and access to the courts after someone has paid their debt to society.
So yes, some released felons didn't follow the process and by law the votes should be thrown out, but you are making the mistake of assuming every single incorrectly voting felon voted for Franken. If you attribute and assign those votes according to the percentages for and against that voted in the general election, which is much more reasonable than your blanket assumption, then Franken still wins.