DFF now support additional tracking variable (Placement ID) support for Shopzilla Publisher Program.
Shopzilla's implementation of additional tracking is a bit different than the affiliate networks and it is not as flexible. You have to SET Shopzilla Placement IDs from your Shopzilla Publisher Account and use those by appending &subid=<
For more information about Shopzilla's Placement ID support on DFF please read the WIKI document above DFF SUBID support. Shopzilla special circumstances are located towards the end of the wiki document.