You have the same question I do, and I don't believe this is possible right now with the current version of Astaro.

This will be something readily available in 7.4, which has been in beta for a while now, and should be due for release soon. Unless you have an absolute deadline, I'd wait for it rather than beat my brains out with 7.3 (or earlier.

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Jon Johnston
Creative Business Solutions
Astaro Preferred Partner
Website:http://www.cbsol.com