This is also why 30 seconds prior to departure setting up the approach to return to your runway of choice and confirming landing distance margin if overweight is time not wasted. If an instrument approach is needed, 4 button presses on the FMGC activates the Secondary and the approach phase.
You should have discussed how to handle an emergency of this nature with your colleague prior to departure and be executing a pre-agreed plan rather than making it up on the go. A lot easier at 0 kts/1 g with no adrenaline in the system!