[launchd-dev] How can I use launchd to do an "at" job ?

"at" jobs are one-shot cron-like commands <http://unixhelp.ed.ac.uk/CGI/man-cgi?at> I can see how to do a cron-like job, but I see nothing in launchd that lets me run something once at a given date-time. “Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us.” Bill Waterson (Calvin & Hobbes)