Hi Erika,
There's not an out-of-the-box way to do this in Marketo, but your developers might be able to set something up using our APIs. Keep in mind these are outside the scope of Support and require an experienced developer. For example with the REST API, there is the Create/Update Leads call:
http://developers.marketo.com/documentation/rest/createupdate-leads/
and the Add Leads to List call:
http://developers.marketo.com/documentation/rest/add-leads-to-list/