Retention Policy specific folder - allow delete

Goal - if folder has retention policy - allow user to delete files/folders - and then hold data in preservation library for retention period

Problem - If we use label + label policy - we can apply at the folder level. BUT users cannot delete anything. we understand this is by design - so we dont want to apply the label to the folder

Problem - if we use retention policy - we can only select an entire library - not 3/4 folder that the policy should be applied to.  So we end up retaining more than required - out of compliance

Can I get some guidance on how to apply a retention policy to a few folders w/in a SPOL library  - AND allow the users to delete files/folders, and that delete data is held for retention period in preservation hold library (or equiv)

Thanks,