You should just delete the referral part of the url, but you will have to build the url someway.
If you are creating your link that opens the form you will have to do build the url either in the form or on your page some how or in an email workflow via sharepoint designer. In a form, i'd create 3 fields, one for the url prefix, one for the form name (must include .xml at the end) and then the final one for the suffix.
http://blogs.msdn.com/johnlee/archive/2008/07/14/url-that-will-open-infopath-form-in-browser.aspx - i htink this is for new blank forms.
and more importantly: http://msdn.microsoft.com/en-us/library/ms772417.aspx