To insert a hanger on a conduit or cable tray, go to
Ribbon: DM Electrical->3D-BIM-> 
Insert Hanger
Pulldown Menu: DM Electrical->3D-BIM->Insert Hanger
You will be prompted to select a point on the conduit or cable tray where a hanger is to be inserted.
Select conduit or cable tray at location to insert hanger:
A hanger will be inserted at the specified point. The location of other hangers will be adjusted based upon the newly inserted hanger.