To use the XA with off camera flash use an optical slave & PC cord.
Small auto flash for the remote, PC cord with optical slave plugged in to the sync end(really?) and tape the slave to the flash for the XA.
Make sure to cover the entire of the flash tube with an opaque tape so you don't have any light leakage. A11 would work fine.
Want softer light? put a layer of lens tissue or two over the remote flash.