Left Side Navigation Substitution on Check Out Pages

Product navigation our site, www.calcompgs.com, is through a <TAG> with  code palced in the Left Side Navigation Template of the Web Site Theme.  Whenever I do not want to display this product navigation on specific web site tabs, I do a tag substitution in that specific tab.  For example, on the Customer Center tab I substitute the product navigation <TAG> with code that includes <NLCOLUMNCONTENTS> so the more relevant links such as View Shopping Cart and account Settings (i.e. Set Preferences, Change Email.Password) are displayed on the left (side).

When clicking "Proceed to Checkout" from the shoppping cart, this product navigation is back on the left and stays through the entire check out process.  In fact, I would again rather substitute out this product navigation <TAG> with code that includes <NLCOLUMNCONTENTS>.  However, it looks as if the <TAG> in the Left Side Navigation Template is used for all cart check out pages.  I would like to do a tag substitution for these check out pages but do not know how/where.  Any suggestions or ideas or heartily welcome!