Hey Monkeysnacks.
It sounds like you've done a fair bit of research! Speaking as someone who had stomach issues a few years ago, I would be reticent to go taking laxatives to loosen your bowels. This could mess up your stomach and make the situation worse, or lead to all manner of other symptoms of irritated bowels- like gas and cramps (not what you want when considering anal).
I would say what you are planning is fine- bowel movement, douche (but don't overdo it) and shower. That's about all any of us can do, right?! Most importantly though- I recommend that you relax about this- not just from the actual act of anal sex point of view, but because nerves may also have an effect on your stomach! (which is another reason that I wouldn't take laxatives). It sounds like you're putting quite a lot of pressure on yourself, and I know you say it's down to it being a long distance thing, but I think just be open with your partner (sounds like you are anyway) and just see what happens- be prepared for the possibility that you may have to wait until next time.
Like I said- I used to have quite a few stomach problems, and now I find if I eat well, exercise (helps everything move through the digestive tract) stay calm (so deal with stress) and leave it alone in terms of medication, then I'm normally fine. And I enjoy anal sex without worrying about it!
Hope that helps :)