Nope. Tried all of the mvs. Everything will work if you use a rex with max_match; however, cannot get it working with auto extracted fields.
I just stumbled onto this and had the same issue last week. I saw a solution posted by Nick here: http://splunk-base.splunk.com/answers/10708/how-do-i-combine-mv-fields-into-a-new-field?page=1&focus...
I took that solution and wrapped it into a macro so I could call it at will from the CLI like this:
eventtype=data | `combine_two_fields(field1,field2,final_field)`
This worked splendidly and is definitely "a keeper."