if you already have WAT on your machine just copy its program folder to a source - sources/$OEM$/$1/here.
it runs portable, no installer needed. the installer gives you an option to install in portable mode anyway.
Winaero Tweaker's SilentSetup.cmd has a list of examples:
cd /d %~dp0
: Install the app silently.
%SetupApp% /SP- /VERYSILENT
: Install the app to a custom directory.
: %SetupApp% /SP- /VERYSILENT /DIR="c:\wt_normal"
: Portable mode: Silently extract the app files to the folder c:\WinaeroTweaker.
:%SetupApp% /SP- /VERYSILENT /PORTABLE
: Portable mode: Silently extract the app files to a custom folder.
:%SetupApp% /SP- /VERYSILENT /PORTABLE /DIR="c:\wt_portable"