Define a series of heuristics.

For example, lets say you have one heuristic that is the number of page views on a particular page, then the number of people who fill out a particular form, then the number of people who.... (Basically various things that should correlate with sales).

The easy way is to then go through and first off measure the correlation between each heuristic and sales and then define some facsimile for the change in sales through something like the sum for all h(corr(h, s)*delta h) with h being the heuristic and s being sales.

You can then use that as a new test heuristic for A/B testing.