I don't know if anyone already does this or if its already mentioned elsewhere on the board but I would like to describe a technique I use to relieve pain during BM's.
I am 'lucky' in as much as my fissure is to the rear of my anus (towards the spine direction). When I go for a BM I rest on my left bum cheek and reach around to my rear with my right hand. I pinch my bum cheeks together with my hand therefore physically holding the fissure closed whilst I defecate. Tightening or relaxing the 'pinch' allows me to control the flow of poop and the pressure on the fissure. It does slow the process down a bit and leaves some residue but its a small price to pay for the amount of relief it gives - after all any relief is good.
This really helps to stop a lot of the pain as the fissure is not being opened up during the BM. Prolonged use of this technique has aided me in the past to keep the fissure closed whilst it heals and stops it from reopening.
It may not work for everyone as I believe fissures may vary in location from person to person, but I hope it helps someone.