Put the free Blitz player in your lineup, anywhere. I used him as third string kick return.
The challenges will place the different Blitz players in your lineup. These WILL count as a second Blitz player in the lineup.
This will satisfy the weekly xp “win games with 2 Blitz players in the lineup”. Any challenge that has you play a full quarter will count. I got 17/20 first run through and then just did one 3x to finish up.
This let’s you get the xp without needing to buy another Blitz player if there’s not one you don’t really want.