Providing that you have control over the ini file, a better solution is:
Code:
[Include]
PCNAME=ProxyConfigX

[ProxyConfigX]
ProxyName=wwwproxy.acme.com
ProxyPort=3128
Direct=*.acme.com
Otherparameter=foo


This way you can have different sections for different proxy configurations.

However the correct way to do this is to use WPAD (or similar) to deliver the proxy configuration to all machines, then use authentication rules on the proxy to determine if access should be allowed or not.