I think I have seen some mention of two different types of Capacitive touch screens. Maybe that is why one type will work and one will not, if I am remembering correctly.
I suppose I might be concerned about the physical properties of the screen itself. A finger will not do much damage, but if you use a sharper object and more force, it may actually damage the screen. This is just speculation so perhaps it would be OK.
I have a Wacom tablet and know how that works. I don't think the device would have to be Bluetooth, just some type of connection to pass the necessary information.
Anyway, good luck with finding one.