Raising the nose at 70kts as you mention, you are above Vmca. But Vmca assumed 5 degrees of bank into the live engine which you will not be able to acheive on the ground. Do what the SOPs or POH specify, then you are covered.
Also, Vr has to be now lower than 1.1 x Vmu (Velocity minimum unstick - in otherwords, the speed the aircraft will fly off the ground if the nose is held up). It sounds like you may possibly get airborne before this and compromise the Vmu criteria.