WireframeSketcher is an offline desktop software so it cannot integrate directly with web applications like JIRA. As an alternative you can export your wireframes as PNG and attach them manually to your JIRA tickets.
If you are using Eclipse then you can try using Atlassian's JIRA connector for Mylyn which brings JIRA to desktop. This way you can have both JIRA and WireframeSketcher inside Eclipse and have an easier workflow. Still, it won't be a very tight integration like you get with Balsamiq.