I had been so unsuccessful doing this with AS with my Hilton Aspire card for years and it was SUCH a pain. Just didn't have any expenses with them that reliably triggered the credit. Had done UA before that but not recently and never got much value from it there either. Love the new Aspire system - a little less valuable but so much more flexible.
But... just got an Amex Plat and was pleasantly surprised how easy it is to use UA credit now! I'm not sure if it was necessary to split it up but I added $50 to the travel bank, four times.
Platinum
United TravelBank
9/12
$50 (x4)
9/22 4x $50 credits
Easy.