We don't get the utm_source,etc. data in CheddarGetter.

I.e.,

Customer lands on our site perhaps with utm_source=PrintAd5

Then they order from CheddarGetter but that data doesn't get passed along.

One way to do that is with GoogleAnalytics and, I think, Passing in the clientID as explained here:
https://developers.google.com/analytics/devguides/collection/analyt...

So,

1. We'd pass in to our link to cheddargetter.com?clientID=XXXXX
   
2. You'd report data to Google Analytics
   
3. You MIGHT be able to retrieve the utm_values from Google.

I'm really surprised that your other customers don't also need this. It's critical when doing Conversion Rate Optimization to know where your revenue is coming from.