Alrighty,

http://www.harobikes.com/mtb/tab2_subNav5.php

Haro mary SS: EBB compatible, nice singlespeed action, with a blanked derailleur hanger. steel. Pink. Black. Metro.

Now, anyone out there checked to see if you can chuck a hanger off an XC onto the SS so you can run a derailleur?

Does it look like anything similar to one of these?
http://wheelsmfg.com/content/view/724/27/

here's a pic of mary XC hanger off mtbr - looking at the mount on the mary SS (slg's) looks like it'd fit

bad news on that thread is wheels don't have a suitable hanger - but you could try ordering a mary XC hanger thru your local haro dealer

PM or wait till Mel see's the thread and ask her to take a photo of the geared and SS mary's that live at her place.
I'm sure that she's looked into it and it would work.