Multiple projects, one CI codebase?

[eluser]theprodigy[/eluser]
The way I have my setup is:

application
--app1
----config
----controllers
----models
----etc, etc
--app2
----config
----controllers
----models
----etc, etc

system
--171
----codeigniter
----libraries
----database
----etc, etc
--172
----codeigniter
----libraries
----database
----etc, etc


public_html
--site1
----css
----js
----images
----index.php //<----- points to application/app1 and system/171
--site2
----css
----js
----images
----index.php //<----- points to application/app2 and system/171

I split my system folder up into whatever version of codeigniter it is running, that way, I don't have to upgrade legacy systems if I don't want to, just because a patch came out.

I split my application folder up into individual site folders

Each index.php points to it's respective application/[site_name] folder and to system/[version] folder