Yes, you can either take a stereo complete mix and use that as the background for him(he can drag into arrangement view) Or you can take all of your tracks and import the stems (again in arrangement view). When he sends them back, he will render just the stems he recorded and give them back to you for import and further processing.
I would suggest he goes easy on compression and post processing if you are doing the mixing. That would give you room to work it into the final mix.