Removing button to show future months after 12 months

[joew]

This is a great calendar and after playing with it for a few hours I think I have got it configured as I wanted it. There is just one thing I'd like to change but can't figure out how to do it... if anyone could help that would be much appreciated.

I show 2 months at a time. When showing the current month and month+1, I don't want the user to be able to click back to older months. For this I used the replacement mootools-cal-public.js as posted by chris in this topic:
viewtopic.php?f=22&t=295

What I would also like to implement is that when showing month 11 and month 12, the 'next' button should not be visible (so the user cannot ever get to month 13 and beyond). How would I implement this? I have looked at the javascript code but I'm afraid I don't have enough expertise to know what to change.

Many thanks