We measure based on source right now with a simple 'how did you hear about us' but I'm wondering if there's a better way to get people who call in to identify w

We measure based on source right now with a simple 'how did you hear about us' but I'm wondering if there's a better way to get people who call in to identify which version of the website they saw. I don't really want to go the 'Mention coupon code AXJM3 when you call to get 10% off' route because it requires us to modify our salon software to match up with the A/B testing software :(