Non-email blind form

I'm created a blind form and need to integrate with a SalesForce button.  This is the link I created so far: http://s1198922134.t.eloqua.com/e/f2.aspx?elqFormName=SalesDemoComplete&elqSiteID=1198922134&emailAddress=<span class=eloquaemail>EmailAddress</span>

How can I tell the form to pass the SF Contact (where a user is on SF) email & ID to the form since this link isn't being used in an email.  Any other thoughts on how to do this?