I haven't tried it but here is how I would go about it.

Take a snapshot of the running VMs to get them in the image list. Then, run 'glance index' to get a list of the images. You will see IDs, names etc of the images placed at var/lib/glance/images.

Then copy the files directly from \var\lib\glance\images to the Essex Cloud Controller and then import the image with all the right metadata defined into the Essex release of glance via glance add.