This can be done by taking a snapshot from xenserver itself and exporting it to a template.
This solution results in a file-based backup of a virtual machine. You can then re-import such vm easily via xencenter. The only thing it requires is some kind of storage to write backups to (cifs/nfs/usb hdd and such..)
Keep in mind this can be slow, as you have to dump all data blocks that have been at least once written and not only currently used space.
For example a new vm with 20gb hdd and only 4gb used will most probably result in 4gb backup file, an old vm which had some writes done, will hit 20gb easily even if it still uses only 4gb of space.
More info can be found here: