Marketplace - Plugin/App 2 installs (two accounts)?

Are IPS able to explain (if possible) how we can run two installations of an app or plugin (if the developer allows)? So, a few of us have the two accounts (for whatever reasoning) and I have a couple of plugins I wish to use but I cannot install via the Marketplace or receive updates. This wasn't an issue before 4.5, but is there a way around this for clients?

Can purchases be swapped/moved over? Obviously, I don't see this being an issue if you have one account and several licences. However, I don't really want to buy the same thing twice.

P.S. This isn't another bash at IPS & the Marketplace...