I found some posts on the old Midwest board, including from 2008 and 2009, which discussed the Companion award promotion in conjunction with the Midwest MasterCard.
From 2008:
Originally Posted by
mke9499
YX standard companion ticket (YX20 award) valid thru 12.31.08, booked at a reduced cost of 15,000 miles, instead of 20,000, using Midwest MasterCard and promo code MCC15.
Reservations must be made thru MM Service Center at 800-314-7125 and is valid for one-time use, only.
This would be a good promotion to reinstate, especially during the slower period at the beginning of the year.