view page using different page template if user source is PPC

Just redeveloping our site and had an idea and just wondered if anyone had done similar. My companu offers numerous financial services and have asked them to rewrite each service as a landing page for PPC campagins.

What I want to do is, lets say a user searches for liquidation and we get our liquidation page showing in organic searches and the same page linked via a ppc add, what I want is that if they view the page by clicking the organic link then they see the page using the standard page template. However if they visit the page buy clicking the PPC ad then they see the same page but it uses our landing page template which makes the page more selling in appearence

I was going to attach a url variable to the ppc campaign ?ppc=true and use $get to check for this and set a cookie accordingly but wandered if anyone could offer advice on where I tell wordpres to check for this cookie and then set the right template

was looking at /wp-includes/template-loader.php