Rolling Time segment

We need a time segment that take current weekday and compare it to average of the same weekday the last 12 weeks.

Eg. One section has xx pageviews this Friday - and to find out if its high or low level, we need the average of the last 12 weeks, on the same day. As we are a news publisher house, we cannot just compair with yesterday or same day last week, as everyday is affected of todays history.

The segment is required to be rolling dates as we wan't to display the numbers in a data visualization app.