How can i test for an environment variable in a RewriteCond

Question

Is there a way to put an environment variable in the condPattern part of a RewriteCond? Here is what i tried:

RewriteCond %{REQUEST_URI} /%{ENV:ALIAS}/(js|css|img).*
RewriteRule (.*) - [L,NS]

But this is interpreted literally by apache (it tries to match %{ENV:ALIAS} instead of the content of that environment variable.

How can i acomplish this?

Bye!