Rewritten url in source code with wordpress installed on IIS

I am using WordPress 3.3.1 with IIS server. to maintain our ranking we used the web.config file to rewrite the url’s to have the .aspx extention and retain the previous url’s.My problem is the oage source shows the original url generated by wordpress instead of the rewritten url.Please let me know if there is a work around to this with out changing the core files.