This will probably be little to no help in identifying him, but it was only thing that's come to me since I first read this. Since the remains were found about 1/2 mile from a gas station, I wonder if he may have gotten gas there and picked up someone who asked for a ride (or who hid in the back seat while he was inside). If so, he could have been passing through from almost anywhere, but his bank/CC records might show a purchase there. It wouldn't have to be the last purchase if he were killed by a male; the card could have been used several times after that without looking suspicious since it wasn't reported stolen.
In spite of the "Minnesota nice" reputation we have, you can be stranded on the shoulder of the Interstate for quite a while before anyone will stop to offer assistance at night. If done later at night when there wasn't a lot of traffic, he could turn on the hazard lights, put a note on the windshield saying he's coming back for the car (in case LE happens to stop) and lay down if a car does approach. If the vehicle was actually a truck, there may have been a tarp in the bed, which could have made it easier than carrying him would be. Even if there was a slight trail from dragging him, most people wouldn't pay much attention if nothing was known to have happened in the area.