I'm not familiar with PushOK, so I can only provide some general comments.
Branching is not a known concept within the SCC interface specification, so any control over branching will have to be done from the PushOK check-out or check-in forms.
It can also be available in an "Option" function. Perhaps if you go to VCS > Preferences and enable the "Show Options for" / "Check In" option, some more PushOK functionality is exposed.