As it turns out, our bodies are kinda cool. I am a bullseye shooter gone ipsc recently, and i think that the sight picture practices carry over quite well.
1. Never Close One Eye - this will cause fatigue, change the way that the light enters the open eye (consistency is key).
2. Dont Occulde One Eye - While i did put a peice of tape over my eye while i was shooting bullseye, i decided that the idea of loosing depth perception while trying to navigate an IPSC course was prety dangerous. (and slow)
3. It costs less in accuracy to keep your sights perfect, but aim at the wrong point than it does to aim at the right point and have messed up sights. (this iis why every one says focus on your front sights)
So the idea is to 'train' your brain to recognize that shooting should be done with the dominant eye.
Some tricks that have worked for me:
If you bring up your gun relativly quickly, looking at the front sight. Get it to the point of aim and close your eyes (both of them). Then open your eyes again, and you should be pointed at the right spot. As soon as things start to get off track (your sight picture changes) close your eyes again. Open em up, realighn (make sure to look at your front sight). Keep doing this for... A VERY LONG TIME. Feel free to take breaks, move around, rest your arm etc, the objective is to get your body to udnerstand and adopt the new behavior. Just like getting in shape, it takes time. Be patient and it will come.
*note* this only works if you look at your sights. if you wander and look at the target, it all gets messed up.
I totaly feel your pain though, i remember how damned hard it was for me to get mysefl to figure out that i should be looking at the sights.... it seems so counter intuitive.