wpkg --admindir ...
The --admindir option lets you change the path to the administration database of wpkg. This path is required for all the INSTALL and REMOVE commands as defined in the wpkg table of commands. Note that the first time this path needs to be initialized with the --create-admindir command.
By default the administrration path is set to "var/lib/wpkg", which is not a root path (it doesn't start with a slash) and thus it gets rooted with the value of --root. When --root and --admindir are left alone, the administration directory ends up being /var/lib/wpkg.
Note that if you change the administration directory for an installation, you want to change it for all the installations and removals to that same target. If you use the --admindir option, you may want to also use the --instdir option.