What works for me: I can't say 'ok, I just need to hold out for two weeks and then she'll go to mikvah'...Because I'm creating an undercurrent of 'I need this' and anticipation. If I need this, I need it now, I can't wait two weeks!
I need to tell myself 'I don't need to have sex today. I need to find something for today to fill that void.' Two weeks time will only come into being...in two weeks time!
Good luck!