You might want to have a look at this SilentInstallHQ page:
Although it is a couple of years old - for a Previous version of PSADT (v3.8.4), the technique is the same as what you are trying to achieve.
You may find this page useful too:
I can highly recommend the SilentInstallHQ.com site as it has numerous examples of apps wrapped in PSADT (v3.x or v4.x) - A great resource!
FYI: I understand Jason Bergner (who runs the SilentInstallHQ.com website) is part of the PatchMyPC team