As for what to do with the little bugger, I don't suppose you'd be willing to go through the effort of creating a well with controlled access that's infected with said bugger's blood? In order to mass produce immortal military and a sealed bookkeeper and manager that never take brakes and will act as the last bastions of sanity in an otherwise berserk or dying fort? Just a thought.
Creating an entire fortress of undead bloodsuckers IS hella-fun! I did that on a succession game after Spish gave me instruction on how to accomplish it, and the results were rather spectacularly bloody for the first adventurer to show up. More so because it was Darkerdark and he has a tendency to make sure his stories are even more awesome.
His post is
here.
Creating the well is both rather tricky, and ingeniously simple. First you'll need a water cistern, empty during construction. It doesn't need to be all that big as the motion of water when it is partially emptied will ruin the well's undeath-giving properties. Maybe a 3x3 chamber. In the middle of it, place a repeating spike trap armed with something sharp, like a metal spear or menacing spike, linked to a lever controlled form somewhere else. The story above the cistern should be empty, and used to access the cistern via a stairwell, and as a housing for the well itself. The stairwell needs to be sealed off so that nothing can climb out of the cistern (very important, because you need to keep your vampire in there, on top of that spike trap, meaning they must have nowhere to path to) and the well needs to be positioned over a hole directly above the repeating spike. Above the well chamber should be a 1x1 room, consisting of a lever-operated floor hatch or bars, and sealed with a door. Once construction is finished, and before introducing the vampire to the spikes, you must fill the cistern to an even 7/7 depth of drinkable water.
Basically, you just need to put the vampire in a squad of their own, and order them to stand in that chamber above the well, on top of the hatch, and lock them in there. They probably shouldn't have any access to the rest of the fort during this time. I'd suggest saving the game at this point so you can savescum if the operation fails (such as if the vamp dies before bleeding sufficiently or dodges the spikes.) When you're ready, pull the lever operating that hatch, dropping the vamp through the well and onto the spike trap in the cistern below. Then, make them bleed, if they aren't already, by repeatedly stabbing them with the spike. Once the square under the well contains a "pool of so-and-so's blood," the well water drawn from it will be laced with said blood, which is the mechanism to spread the curse. Then just convince the portion of the population you want to infect to live around that well, with no other drink source, and before long at least a few of them should start sucking blood.
I am not responsible for the destruction of your fortress if it is destroyed via tantrum-spiral when everyone is eating their friends. You'll just have to find some other means of keeping them blissfully unaware of what's going on around them.
Also, if the original vamp survives the procedure, you can extract them form the well, offer them whatever medical attention is necessary, and then lock them up or something. The well will probably get ruined by the motion of the water flushing the blood stain off the square under the well, so you might have to set up a new one if you don't get as many vampires as you would like. I think I succeeded in infecting ~25-30 dwarves. Who promptly drove the fortress right into the ground when it came time to sate their thirst.