Hey Nitin,
Prior to wyBuild & wyUpdate 2.6.15 %urlargs% can only be used on update sites. So, until wyBuild 2.6.15 is released, you need to add 2 sites to the download site list. Then right click one and make it "Just a server site", then right click the other and make it "Just an update site". Use %urlargs% in the "Just a server site".
Does this make sense?