Serving from different directories for Internet Explorer

We have two different versions of our website – one for older versions of Internet Explorer (7 and 8), and one for all other browsers.

(arguments around JS feature detection have been made, but we have found it easier to progress this way!)

We would like to silently (ie without a 301) files to be served from a different directory – so a request to:

/app/foo/bar

would be served from the directory:

html/ie/foo/bar

for Internet Explorer 8 and below, and for other browsers from:

html/other/foo/bar

Is this possible to achieve using .htaccess?

/app/
  - index.html (for modern browsers)
  - .htaccess (with remapping for IE 6-8)
  /ie
    - index.html and other files
    - .htaccess (to turn off further remapping efforts)

RewriteEngine on
RewriteCond %{HTTP_USER_AGENT} "MSIE [6-8]" [NC]
RewriteRule ^(.*)$ /app/ie/$1 [PT]

RewriteEngine off