This is a true "nightmare scenario" and really approaching -- if not beyond -- the limits of the realm of CRM. The assumption of CRM is that while pilots can get task saturated, focused on "making it (the approach) work out", and otherwise lose track of the situation, everybody is willing to listen to reason, if it is just presented with sufficient clarity. If a pilot is so far gone beyond that point that he is absolutely determined to take his approach to its completion, you're approaching a different scenario.
Let's stipulate at the outset that this sort of a scenario is incredibly rare. Good pilots can get so focused on making things work that they lose situational awareness, but a clear statement like "we're 40 knots fast & two dots high on glide slope, GO AROUND" will typically snap pretty much everybody out of it. The captain who is so wrapped up in his authority that he's willing to ignore an FO's repeated direction to go around is pretty rare.
That said... in the nightmare scenario, the FO's options become:
- Keep making callouts, more directive, more urgency, yell louder.
- Tell ATC that "we need to go around" on the hope that ATC directing "Flight 123, go around, fly runway heading, maintain 3000 feet" may accomplish what the callouts didn't.
- Raise the landing gear.
- Push the power up or otherwise fight for control of the aircraft.
- Attack the flying pilot, perhaps with the aircraft logbook (metal cover) or a heavy flashlight or some other improvised weapon.
At this point, the FO is in the awful spot of having options that have a limited chance of success and in several cases, huge risk of making a bad situation even worse. There is no "policy" solution to this sort of a scenario. That a captain would have ignored repeated GPWS callouts and FO callouts is beyond the realm of what policy ever imagines.
As I said before, this sort of scenario is almost unimaginably rare. Pilots just don't often reach the level of being an airline captain without sorting out the need to accept a "Go Around" callout from their First Officer. Are there arrogant pilots out there? Absolutely. Arrogant enough to get to the situation mentioned in the OP? Very, very, very few, and very far between.