I think a lot of that comes down to how you rejected the first job. I mean, were you like "lol got bettar job, FU" or were you respectable about it? If the first, I think you're pretty sunk. If the second, you probably have a better chance. Just say things really did not work out with the other job, and that you would like to inquire about the job that you unfortunately were unable to accept, to see if there is anything similar that you could possibly apply for. Make sure that you make it known that you don't think you're just gonna get the job. Make them realize that you regret passing it up, and that you would like to go through the application process again. They like that shit.