Enable users to add tracking code to head on specific pages?

We have clients that need to add yahoo ppc conversion code to their thank you page so that when PPC visitors fill out a form and are forwarded to the thank you page, the PPC conversion is tracked.

The issue is that the code can't be placed in the thank you page itself, but needs to be placed in the head of the page. We have a header / footer plugin that can placed code in these areas, but this occurs for every page, not a selected page like a thank you page and placing the code of every page would obviously skew the conversion data as every page would hit as a conversion.

Anyone have any ideas on how to enable this option for users? I'm thinking headspace might be an option for targetting the head of a specific page, but would REALLY prefer to not open that can of worms in terms of supporting the plugin, it's awesome, but I envision LOTS of support questions should we enable it.... it's just too high end with too many options.

Any feedback appreciated!