Thanks for your suggestions. We have this in backlog for quite some time. Now when we know someone is interested in this we will plan it into the development.
For your other question. For now, you can create config file manually in the .vs folder, but for now you would need to start the server yourself from command line. Something like:
iisexpress /config:c:\projects\phpproj\.vs\applicationhost.config /site:MySite
And set up PHP project to the custom server so it would point to the virtual directory configured in your applicationhost.config
Please let me know if that works.