We have talked to them and just had a reply as follows;
We gauge demand based off of tweets, hash power, length of bitcointalk thread, volume on other exchanges, etc. Follow us on twitter @bittrexexchange and tweet about how much you like this coin and Bittrex. We respond to creative and insightful posts to help market your favorite coins and Bittrex. I'd also consider coming to our irc channel #bittrex on irc.freenode.net and do some guerrilla marketing. The traders there can help you gain exposure for your coin.
Thanks,
Ryan @ Bittrex
Follow us on Twitter: https[Suspicious link removed]xchange
So let them know if you want to see ZirkCoin on Bittrex, we are working in the background to get some alternative exchanges onboard also.