Put this on the end:

&sourceid=navclient

So that your URL is like this:

http://google.com/search?btnI=I%27m+Feeling+Lucky&q=6920927181221&sourceid=navclient

Put this on the end:

&sourceid=navclient

So that your URL is like this:

http://google.com/search?btnI=I%27m+Feeling+Lucky&q=6920927181221&sourceid=navclient

For example: Stack Overflow, which when clicked will have the HTTP REFERER header set to http://superuser.com/questions/56021/[...]. The same link sent through email, or when opened using right-click » Open Link in New Window, will have no REFERER set at all (in most browsers). All seem to work fine.