Create New Lead on List Import

Running into a problem setting up workspaces and partitions.  I imported a list and found that a few of the leads being imported into one workspace already existed in another workspace as a contact.  Because it existed as a contact already in another workspace, Marketo automatically used assignment rules for the existing lead.  What I need to happen is for Marketo to create a new lead in the partition I am importing the lead into.  I need the leads in each workspace to be treated as a new lead even if they exist in another workspace.  Anyone have any tips on how to resolve this?