I don't see how to give a blood spirit endowment, even as a free spirit. If channeling the spirit, when using the spirit powers, I would argue that the spirit receives the Essence or the magician starts losing 1 Essence per day.
To supplement Michael's point about magic loss being tied to Essence loss, not current Essence value, the Essence Drain power doesn't increase the maximum Essence so even if the character could benefit from the essence gain, he would start at 6, gain 1 to still be at 6, lose 1 to the implant, dropping to 5 essence and a maximum 5 magic. Draining 1 again may take him up to 6 essence, but leaves his magic and maximum magic unchanged.