Softbox for EF-X20 flash

Application: I will be doing some informal portraits in an office environment (in individual offices that are approximately 10' x 10' in size) with my X100 and EF-X20 flash. I'll use an off camera hot shoe cord (similar to a Canon OC-E3) to move the flash off-camera.

Question: Has anyone used a softbox with the EF-X20? I need to find a decent one that can be made to fit my flash. I don't have it right in front of me, but I think the cross sectional dimensions of the face of the flash unit are something like 1"H x 2.25"W.