PackageMaker - Accessing Model Identifier & Creating custom failure error messages

Question

I'm using PackageMaker (ver 3.0.3 on Leopard 10.5.8) to install an application and want to check the Model Identifier & CPU prior to installation. The application does not work with certain models of MacBookPros. I've tried to use a pre-install shell script where I grab the system_profiler output and grep it for specific Model Identifiers & CPU and exit 1 on detection of the unsupported models, but it doesn't give a satisfactory or user friendly error message upon that exit. It gives the generic failure / contact the manufacturer message.

Does anyone know if that information, i.e. Model Identifier / CPU is available as part of the "Requirements" Tab in PackageMaker which would allow a more custom and graceful failure message for the user.

Thanks