I know it's been said like 500 times, but... couldn't use Party Finder to set up your own parties? i see a lot of PF telling "full run" on them, so it shouldn't be an issue.

Yes, sucks if you find this kind of idiots on Duty Roulette, but... "wasting the soldiery bonus"? you don't waste it until you complete the dungeon. If you don't complete it the bonus doesn't dissapear.