[galraen]

I looked at the scripts for the vampire cure, and it sets the PCVampire variable to -1

Set PCVampire to -1

, if you're playing on a PC you could try using the console to set the variable to 0 or 1. Zero being a non-vampire, thus (I believe) allowing you to become one. One should mean you are a vampire, but probably will not work properly as the relevant effects have not been activated.

I suggest making new save before experimenting, and try setting the variable to zero

Set PCVampire to 0

, then contract the disease.