Thanks for the suggestions, I ultimately went a different route with this, and bound a slider to the variable that was previously at the top of the page (which was 30 in the first instance) and allowed the user to select how many days worth of data they wanted to see:
The text box is also editable, so they can manually type a number in, if they wish (the '500' example at the end). I did use some of the styles suggested to modify the axes to a different grey to lessen it's impact upon the page, but it also meant that the X-axes date was relevant again, so the requirement to remove it changed (let's just call it 'agile development :). The slider modifies about 10 graphs across the page and works quite fast.
Cheers
Richard