Hi. What you're looking for is what's known as a ChoicesChanges xml file. I would start here for some good examples of how to determine what choices are available in a package and how to create the xml file that chooses the items you want to enable/install.
That link above is not the only example nor the only thing you should look at, but it's a place to start.
Overall, what you want to do is open Terminal and run something like the following against your package to get an idea of what choices are available.
installer -showChoiceChangesXML -pkg /path/to/Installer.pkg
Then follow some of the steps in the link above to determine how to add those choices into an xml file. The bottom line is, the only way to customize the installation, if you want to stick with using the vendor supplied installation package, will be to script the install and tell command line installer to use your choices file instead of just installing all options.
Hope that helps.
