I might have an odd solution.
One of my vampires, a few games ago, got infected by a weretortoise-dwarf-child (That was a child tantrum to remember!) I didn't realise he had, and when he got his "spells" he would go down for a few days to the catacombs and visit his tomb (he never went into his bedroom, he liked his personal grave better) and turn into a weretortoise, and turn back again, head up the staircase and do his job.
This happened for multiple months: I had no idea until I was overseeing a mason who was in a mood, months after the infections, I thought, had finished. The moody mason was down in the coffin-making mason workshop for some reason (I seem to remember he made a chair, it definitely wasn't a coffin or a slab, the only purpose I ever actually put that mason workshop there for originally)... Anyhow, I'm watching the mason mood away, when the vampire carpenter comes past, goes to his tomb, on break, turns into a weretortoise right there on my screen, wanders around his tomb for a bit while I pause and stare and set it to run again and stare and pause and check whether anyone else is a weretortoise, and let it run again... then turns into a dwarf and walks back out of the catacombs, past the moody dwarf who is whinging about not having any cut gems or something, and goes back to work.
I put it down to being weirdness at work, but I watched it happen for a few months afterward, before the fort died of framerate issues. I've not had a vamp-were double infection since.