This is not done in the template. Each Page (and More Info Page, for products) has a File Name setting. If you include the directory name (must be a subdirectory of the main output directory) in this setting, then ShopSite will publish the page to that directory (must already be created, ShopSite won't create the directory).
So if normally your ShopSite-generated pages are at:
http://www.mydomain.com/
and you want to put a particular page in:
http://www.mydomain.com/sub1/
Then in that page's File Name field you would put:
sub1/mypagefilename.html
Assuming that the sub1 directory already exists and has writable permissions, then the resulting URL to your page after it is published would be:
http://www.mydomain.com/sub1/mypagefilename.html
-Loren