wpkg --root ...
The --root option is used to specify a path where the installation root (everything) gets installed. Note that the first time this path needs to be initialized with the --create-admindir command.
By default the root path is set to "/".
Under MS-Windows, it is customary to change the root path to "C:/Program Files/<company name>" so the installation goes to the directory where installation files are expected to go for <company name>.
The --admindir and --instdir options can be used to change those two directories. Note that when both of those options are used, it renders the --root option useless.