Post them somewhere else, giving yourself some backlink rank.
I do have a few questions though...what reason did they give you for rejecting them?
If it is for ' having too many submissions on that topic right now ', post them elsewhere and focus on resubmitting tighter microniche targets in your content.
If it was for something like word count or some other error on your submission, be sure and rework it and resubmit before posting it publically. If you email their editors, they will tell you what the reason of rejection was.
People miss out on a lot of money from that service due to simply not stopping to ask ' why? ' and fixing that issue, making their article perfect to get paid, rather than wasting it by simply posting without checking.
Always check that out first. After you bug them with a couple of rejection inqueries, they will start to post it to you in your rejection emails, if it isn't already there to begin with. I remember their reason always being there, as generalized as it is, it covers the point.