I have, just to prove that I could... it wasn't impressive, though. There isn't enough throat space to move the quilt enough for my style of quilting. I used the plastic plate to cover the feed dogs, which worked fine, and the stitch was good without much tension adjustment.
My biggest problem with FMQ on small machines like the Jem Gold or my featherweight is that your hands have to be really close to the needle because of the small throat. I quit trying to do this "just to prove that I can" when I sewed through my finger while free motioning on my featherweight.
From what I recall the internals of the Jem Gold are about as strong as on full size Janomes, so I wouldn't worry too much about it not being able to handle it... however, I think you might be a lot happier to look for a $20 old Singer on Craigslist than risking overstressing your Jem. The Singer 15, or a Japanese clone of it, are supposed to be great machines for free motion quilting on.