Google AdWords: Code placement on virtual pages

We have an application written in CakePHP that dynamically generates AdWords conversion tracking code towards the footer of our page. The reason for dynamic implementation is that forms don't necessarily take the user to a single static page; but rather, the user can be taken to multiple pages where the same tracking code should be implemented (on the fly). For example, when a user purchases, he can either be taken to 1) a list of his purchases or 2) coupon. The way we currently handle this is by setting a session variable in the post purchase logic. When the next page loads, the AdWords conversion tracking code is loaded in the footer of the page. The issue we're experiencing is that there's 30 - 40% discrepancy in AdWords reporting vs. sales figures. We need someone to consult us on the best method of implementation (since ours isn't working), and also for someone to implement a proposed solution in our current code base. You will need to be proficient with SVN as we will provide access to one. You will also need to be available for work immediately.