Howto inject new Handler DLL into the config from Install/Setup(msi)

Hi

I have created a BarCodeReaderHandler and need some info on how to install it correctly.
I used the documented approach to get Registry variable(SOFTWARE\\Intel\\HelthcareSDK\\bindir),
and use that for the install path.
Next problem is how to "inject" our handler into the config ?
I can't just replace the config file and call it done(I found out by trying)...
I need a way to set our handler as the default from the install.....

Thanks

JR