I pondered on this same issue for ages. As a temp fix i have a cable tie that works as a....uh hem....switch.
As a more permanent solution i was planning on building something that would encompass the pointer with some kind of mechanical switch etc.
In the end i found that someone has made one, and i got one second hand on ebay. Im hoping that it will give me some idea as to where it came from.
See this link for the one I got:
http://cgi.ebay.com.au/ws/eBayISAPI....MEWN:IT&ih=017
If anyone knows who makes these, or where they can be purchased online....pls post.
Daniel