Hey Andrew!
Great question – and great timing, too 🙂 We have a new Multisite License launching on the site very soon, which will let you license one network installation of WordPress (regardless of the number of sites on it).
I don’t have a specific launch date for the new license at hand, so it could take up to a couple of weeks from now before you actually see it on the site. I totally understand if that’s too long to wait for a “proper” license, but we’re happy to help you out in the meantime – shoot us an email at [email protected] and we can help sort things out from there.
Cheers,
George