Cancel uninstall (InstallShield custom action)

Cancel uninstall (InstallShield custom action)

I inherited an InstallShield Basic MSI Project and I am trying to cancel
out of an uninstall, but the uninstall still proceeds until finished. A
dialog shows the progress of the uninstall and upon clicking the Cancel
button, it pops up a CancelSetup dialog that asks if I would like to
cancel the uninstallation. When clicking "Yes" a custom action is called
that calls an InstallScript function that just returns
ERROR_INSTALL_USEREXIT. The CancelSetup dialog closes, but like I said,
the uninstall progress still continues until uninstall finishes. I'm
wondering if there is a command that can let the Installer know to abort
the rest of the uninstall and then would rollback from there.
Note: This is not a question about rollback, so please don't reply with a
response about rollback.