InstallUtil: custom options

I have 2 questions about custom options in InstallUtil.

The help screen for InstallUtil says this:

--- quote ---
Options take the form /switch=[value]
<...a list of options follows...>
Individual installers used within an assembly may recognize other options.
To learn about these options, run InstallUtil with the paths of the
on the command line along with the /? or /help option.
--- end of quote ---

The questions are:
1. How do I get the custom options passed into InstallUtil?
Suppose I type a command line:
installutil /x=a /y=b <assembly_name.dll>
How do I get "x=a" and "y=b" in my class?

2. How do I pass the information about supported custom options to
InstallUtil, so that
it is available from "installutil /? <assembly_name.dll>".

Thank you.