No, you can not do this. However you could use tinyurl and format it like this
http://whateverYouWantToSay@tinyurl.com
Web browsers usually ignore anything before an @
therefore you could effectively hide the actual site being linked to, as long as your friend does not know that.
What actually happens is the data before the @
is submitted to the web site in the form username:password
. However it must be a site that requires authentication to access, or the site will normally just ignore it.