Just. Use. The. Offset.
It's safer than using a constant value, since it allows the motherboard to still compensate for load and Vdroop. It's like all the benefits of overvolting for overclocks, without the drawbacks of a forced constant voltage. Instead of giving it a set value, you tell it how much more voltage to run over stock. Super convenient. Also, I wouldn't push very far past stock voltages with a BCLK overclock of that nature. Who knows how good that CPU is at handling extra voltage, especially since the internal memory controller can be very picky.