Right now it's not possible.
I welcome patches, but development has stalled as I have no time right now.
It would need a database schema change (adding an expire date) and the management of it.
Or maybe better add a "user_options° table and create the hooks for plugins to add features and functionality to user management. (i.e. password expire also comes to mind, but could also be used to have additional fields for registration and so on)
This would need more work though.