Possible to assign more than one site to a Pro-site subscription?

Hi all,

I've had a dig around the plugin and can't see if this is possible but...

Is it possible to allow a subscription to have more than one site? e.g. configure a subscription so only one site is possible, but also configure a subscription that allows the subscriber to have, say, three sites?

If not, is it in the pipeline?

Ta
Andy.