interpolate other ${project.*} variables in the site descriptor

I'm trying snapshot version from site plugin (skinning is a great idea !!)
But I have trouble with urls
example project.url = xxx
in my site I had an menu with item.href=xxx:8080/path
the generated url is : http://xxx/:8080/path
An other trouble I defined bannerLeft with <href>${project.url}</href>
When I naviguate in the site the bannerImage has a link with ${project.url}/currentPage