Can you elaborate on what you are trying to do?
I don't believe it's possible to specify a request header via a link. You can send GET parameters to the target site with the following notation:
www.google.com?q=searchterm
The first GET parameter is separated from the URL by a question mark (?) after that each additional parameter should be separated with an ampersand (&) like so:
www.google.com?q=searchterm&otherparam=value&otherotherparam=value
