Hi Niels Erik,
It should be possible to delete submissions without applying any patches at all (the top Bugzilla entry you linked is intended for OMP pre-release and the relevant code should already be included in OMP 1.0).
As for tasks, the code in bug #8528 will add a row action permitting the deletion of tasks from the Tasks list in the dashboard. However, as I say, it might be easier to wait for the release of OMP 1.1 (which we hope will be within a month, depending on our translators' progress).
Public Knowledge Project Team