That isn't how physics work, when something boils it boils. Also when you factor in heat transfer coefficients then the liquid oxygen in tank is actually "heating" the liquid helium pretty substantially as it has considerably higher heat conductivity than air. ;) The analogy of boiling water into boiling oil is pretty close one as far as the process goes, the boiling oil would evaporate the boiling water instantly and things go boom, the liquid oxygen would evaporate the liquid helium instantly and things go boom.