regular expression in http.conf

[fla_dolphin]

I am trying to "proxy" all client url requests except those that are
on the local web server.

The following in httpd.conf works (sort of):

<Directory ~ proxy:http://[^1].*>

this will allow any url request that begins with "1" to be served without asking for a passwd

I need to be more precise and alllow ONLY requests begining
with "192.168.1."

I've tried these and they do not work (does not ask for pswd):
<Directory ~ proxy:http://[^1][^9][^2]\..*>
<Directory ~ ^(proxy:http://[^1][^9][^2][^\.][^1][^6][^8][^\.]).*$>

Question: what regular expression can I use in <Directory> directive in httpd.conf that is equivalent to:
^proxy:http://!(192.168.1.).*$


Additional info:

relavent httpd.conf:
<Directory ~ proxy:http://[^1].*>
AuthType Basic
AuthName "Enter Internet Access Password"
AuthUserFile /made/up/proxy.pswd
Require valid-user
Order deny,allow
Deny from all
Allow from 192.168.1.0/255.255.255.0
</Directory>

Intranet web server on port 80, separate proxy server on port 8080 all on same machine, with same docroot.

Thanks