This is ridiculously anecdotal, but I asked a yoga teacher how to make it more comfortable to sit with legs straight in front, and I was expecting some kind of static stretch.

She said to do leg swings back and forth, which I remember I did years ago in Taekwando. I find doing those leg swings really nice for loosing up the hips and all that and as an antidote to office sitting. I also like that I don't need to stretch per-se.

Ymmv, I am not a physical therapist etc. etc.