[NTG-context] Frame until the bottom of the page

Hi, I want to create a frame that should occupy the remaining space on the page. For example, if I call this frame when the page is 1/3rd full, I want the frame to have an height of 0.667\textheight. How can I do that? In other words, how to I find out how much space is left on the current page? Thanks, Aditya