2 other Options... Amtrak and ATA
Ok, a little unorthodox for a UA flyertalk forum, but I'd suggest also looking into Amtrak which has one train a day (r/t is $40) or ATA to Flint.
The fare to FNT is as low as $83 r/t, FNT is right on an interstate and is a about a 45 min. drive to Lansing. Their FF program is simple, fly 3 r/t and you get a free companion ticket in the US, 6 r/t and you get your own free ticket, so for $600 you get a free ticket in the US. Something to consider.