Good question, but we don’t have a good answer. The subscription is associated with the user that placed the order, and that’s the only way we have to track who has active subscriptions.
It’s possible (I’m pretty sure) for you to add them on any support tickets you open, by clicking “Add or Remove” on the message, so they’ll be part of the conversation, but your account would need to open the ticket. I guess they could also open a ticket and include the serial number and your username, mentioning that the license is on your account instead of theirs. We don’t prevent any user from sending a staff PM, we just usually close those from GPL users; but if it’s made clear in the first line that it’s a license owned by another account, and we have some evidence that’s true, that would also work.
I’ll try to come up with some way to better handle this; we use an off-the-shelf (mostly) commerce and user account (WordPress with WooCommerce and some custom modules) system that doesn’t try to address this need. But, I can see it would be a pretty common need for hosting providers or companies for anyone in the org to be able to open a support ticket.