Filler Cells and Substrate Contacts in Virtuoso GXL

Hi,

I am using the student version of cadence tools at my Univ to auto place and route a custom design, using standard-cells. I am using the Custom IC tools suggested, i.e  Schematic XL and Virtuoso GXL. I design the schematic of the architecture, first, then using the connectivity driven option, i generate all the corresponding layout cells. I have a query regarding the Custom Digital Placer. (I am working with the GUI, not any commands)

How do I insert Filler and standard cell substrate contacts in the layout? I read the instructions in the documentation. When I created a custom Std Cell Sub contact, and put it in the layout file, I can't label it as substrate contact component because it is not in the schematic. When i make its put a corresponding gate in the schematic of the design, I get an error saying it should be of type STDCELL. I would appreciate a description of exactly where and how to place substrate contacts and filler cells.

thanks