You can do sit ups with the soles of your feet touching to take out the hip flexor. Sometimes called butterfly situps.
Jill Miller Smashes Your Guts! (and psoas, and tacked down viscera, and matted down abdominals…) Part 2
Episode 301: Psoas Flossing and Biker Hips
Episode 129: The Twin Bowstrings, the Psoas and Scalenes
Episode 75: Your Inside Psoas Bits, World Record?
Episode 40: USAW Oly Prep: Some New Hip Love /Psoas/Calves
Episode 26: Hips and Seppuku: Psoas and Hip Soft Tissue Mob