Telescopic lens for optical mouse sensor

Hi, just wondering if anyone has put a telescopic lens in front of an optical mouse sensor so that the positional sensing can do optical flow on a surface 20-50cm away, instead of 5mm away? I've been looking at these: http://peauproductions.com/store/index.php?main_page=index&cPath=26_4 and then also stuff like this: Amazon.com and I'm just wondering if anyone has magnified IR images at that range or knows that it just won't work, etc. I don't mind buying a few and trying them out but I'm curious if anyone has any light to shed on it before I pull the trigger. Thanks!

Never tried, but sounds like fun!