I think habaneros would be a bit strong. One thing I'm thinking of doing is just getting some anchos, a serrano and good dark chocolate and melting the chocolate over a double-boiler. Then, puree the anchos and seranno and add to the chocolate mixture. Then strain through a fine mesh strainer.
This could be done a couple of days before brewing. Plus, it gives an opportunity to taste the mixture for heat and flavor before adding to the kettle.