How I do it is as follows:
1. load your save
2. select Joe Average as the active manager
3. go to the MANAGER tab and select ADD/ EDIT HUMAN MANAGER (does not have to be an online league for this method to work)
4. Click ADD ADDITIONAL MANAGER button
5. Add your PERSONAL INFO and select which team you want to control
6. Click OK button.
go back to the MANAGER tab and select your preferred manager.