Well, it probably depends on what your view of the Blood is. If you think its a secret group that's infiltrated ComStar/WoB and behind everything, then I would simply use the Terran affiliation and the WoB affiliation. I'd add in an "In For Life" and probably a Dark Secret or two. Not to mention some interests like "Writings of the Blood" or something similar. I wouldn't really expect it to be too much different.