The URL tag is the supersize stored version of the image with the _o.jpg name format (as example). You could anchor your image to your your own blank page with the supersize.
If you want to specifically use Auctiva's Supersize page, you need to link using their showimage.aspx? query string format, where they pass the image ID numbers to build the page at the server. Just build a listing with their format and use Preview to look at how they make the page call from the anchor tag. As you can see, it's not something the URL tags alone can produce. Using Javascript to build the page code dynamically or with href calling a script with the image list as parms are possibilities I've considered for a widget, i.e for a custom situation like your requesting.
Template widgets are just what the doctor is working on.
Danno