custom javascript for previous/next month links in <asp:calendar> control

I need to change the JavaScript that the <asp:calendar> control generates for the previous/next month links. I don't need to change what it does - just how it's written and how it behaves. I have the control load into modal dialogue window but clicking on the prev/next month links causes a new window to open with something like "javascript:__doPostBack('MyCalendar','V3135')" in the url and the control does nothing. From experimenting with the day links, which used to open a new window as well, I think that changing the links to <a href="javascript:;" onclick="__doPostBack('MyCalendar','V3135'); return false;>" with a dynamic date value will probably fix the problem, except I can't figure out how to make this change. How can I manipulate the script in these links? Or is there some other way to make the calendar behave and not open bogus new windows on me?

Thanks!