I've been wallowing in Spike/Xander slash for the last few weeks. Alas, I've lost a fic that I could have sworn I bookmarked... I've been trolling through Delicious and all the other sites I generally haunt without success.
While this is only a (relatively) minor plot point, it may be enough to identify the fic in question (without spoilers for the tale) - Xander takes Spike to open an account at the blood bank, which will provide magical stasis for the safe storage of Sire's blood, as well as arranging regular deliveries of bagged human blood. It's the only tale I've read which features 'accounts' at the blood bank like this.
Thanks for your help!