I once had a similar problem. The properties file was used by a Java program, in java.util.Properties format. I used Config::Properties, which worked nicely for me.

I also couldn't install modules on the machine, so I distributed the module with the script, by putting Properties.pm into a subdirectory lib/Config and told the script to use lib 'lib';. See lib. If your current directory isn't the directory that contains the script have a look at FindBin.

Hope that helps a bit.