Toggle two AJAX Calendar Extenders

Hi

I have two AJAX Calendar Extender controls, which populate a textbox each, one for a from date and one for a to date. What I am trying to achieve is when the from date is set to add 7 days to the to date, and if the to date is clicked and the date changed, to respectively set the date in the from date to be 7 days in the past. The overall effect I am trying to get is that the dates between the two controls should only be 7 days, i.e. a week.

Trying to search on this, I am not seeing any examples, has anyone tried this, and if so, how can I do it?

Thanks