Create dynamic subdomain like path using URL Rewriting

Question

I've URLs in my website and which are using query string values For example:

http://foo.com/xyzPage.aspx?barvalue=yehaa
to
http://yehaa.foo.com/

Please suggest how it can be accomplished without actually creating subdomains on server ..

I've IIS 7.5 installed on server machine and using Asp.net 4.0