there really is no way.
From a programatic stand point you can do Shortcut Expiry set to a year and then archived item expiry for 2 years or whatever the retention category is set to.
The way we are starting to do it though is to use Virtual Vault exclusively and not create shortcuts at all, and to delete all existing shortcuts.
This keeps the mailbox size down, and the fragmentation levels on the exchange server down, makes it quicker to rebuild OST's etc, so the exchange team love it
and from the users perspective, the Virtual Vault behaves like a PST and we've found that most users shove their mail in to a PST already anyway, so the transition to virtual vault is really easy because there's no change in behavior
That and the ability to create rules to move items straight in to virtual vault, everything works nicely
Unfortunately for what you're trying to do with out VV, its just not possible
https://www.linkedin.com/in/alex-allen-turl-07370146