Site Specific Subdirectories

One point I had not thought about for awhile was having site specific webpages in site specific subdirectories. The difficulty is that you want the url to be fairly seamless. I solved this in my previous design, but in that system you never saw the url. So the potential solution I am currently thinking of it conditional redirection. When you get a url request you check to see it it exists. If it does you tack on 'site=XXX' for uniformity and pass on the request. If it does not you rewrite the url to remove the extra directory and tack on 'site=XXX'. This, or course, may cause havoc with the paths. But it will probably be solvable havoc. This also reduces the generic nature of the redirection module, but since this module is a fairly small amount of code I am not too worried about it.