On Ubuntu some apps call /usr/lib/policykit-1/polkit-agent-helper-1 when it needs to execute "privileged processes". This is inconsistent with gksu force grab behavior where the whole screen is disabled unless user cancels.
Is there any way the former could be made to have a force grab to make it more consistent with gksu?
If it's consistency and not specifically gksu-like behaviour you're after, you could go about it the other way round by using gksu-polkit instead of gksu.