  Protomagnetars spun up to millisecond rotation periods by supernova fallback
are predicted to radiate gravitational waves via hydrodynamic instabilities for
~ 10^2 s before possibly collapsing to form a black hole. It is shown that
magnetic funnelling of the accretion flow (i) creates a magnetically confined
polar mountain, which boosts the gravitational wave signal, and (ii) "buries"
the magnetic dipole moment, delaying the propeller phase and assisting black
hole formation.
