The PeoplePicker is probably the issue.
Why not do away with that and use a generic data source structure with UserProfileService or Qdabra's ADWS to fill in the people's names.
Then, you could use eval-eval - see this link:http://blogs.msdn.com/b/infopath/archive/2006/04/05/569338.aspx
Of course, the workflow could also do it by extracting the field data from the form. I think that you can do this in stock SharePoint Designer workflows, but if not, you can look at Nintex or write your own in Visual Studio.