Same job, spending long hours sitting. What i started to do for a few months is to stand up every hour for 5 to 10 min at a time, I am lucky we have convertible (to standing & sitting) desks where I work. It has made some difference for me, in the sense that i feel slightly less tigh in my hip flexors and hamstrings but I can’t say that i have suddenly become more flexible 🙂 although my range of motion has improved quite a bit. Hope this is useful 😉