second/overlay rails root directory ?

Hello Folks, is there a way to have rails look for files from 2
different root directories ?

Heres the scenario...

- we deploy our apps to lots of customers
- they each have a few customizations (views, configs, css, etc)
- I would like my rails to look for files like this

- first search RAILS_ROOT/overlay/customer1
- then search RAILS_ROOT like normal

so if nothing was in the overlay directory, all the files would come
form RAILS_ROOT like normal
- but if RAILS_ROOT/overlay/customer1/app/welcome/_message.rhml
existed, it would use that

Or am I in left field here ?

This seems easy to do assuming rails finds files from one centralized
place, then you could just add this functionality there.