This is a good question, a year back or so, even I was facing similar problems with a website at work. We wanted to track not only campaign and ads on conversions, but also which keywords are leading to higher conversions. Here’s what we finally did.
- Changed the Destination URL in all the ads to include the {keyword} parameter
- On the landing pages of my ads, we create a SESSION and store information such as the gclid, the target keyword, country of origin
- Now whenever the user clicks on the form or other lead capturing mechanisms, we access this session and retrieve all the required information
Using this method and tracking which leads are finally converting into purchases, we are now able to find out profitability of a keyword over a period and even the average Lead to Cash conversion time.