Can Dataload or Bulk Import webservice in upsert?

We are trying to change our interfaces process from Import via webservices to using Bulk import (like Dataloader).

Our Webservices import were flexible enough to manage upsert of data.

Now with Bulk import (much faster)  we have to either provide file with only new records, or with only existing records, in order to pass the "Insert", OR "Update" Parameter (sorry I'm not the technical guy)

Do you know a workaround in order to avoid managing 2 sets of imports?

Do you know if can post an ER to do so?

Thanks

Isabelle COLAS -

Sodexo Global CRM Application Manager