I'm in a similar situation, maxwello, and I think if I could do it again, I would:
retake the prep courses that the top schools require (linear/matrix algebra, stats, etc.)make sure that I aced the quant section of the GMATrekindle relationships with profs from my MBA program -- can you do any research for them?above all, build relationships with profs at my top pick schools, and see what they recommend
Having said that, though, I would also take a close look at the current student body at the schools to which you applied. Some programs just may not be interested in older students, however unfair it may seem.
Good luck!