I saw a big plastic hypodermic/syringe looking dispenser at Walmart in the auto or hardware department I think. (Maybe it was for agricultural purposes, & it only cost a 2-3 bucks). If you filled it up with bore butter, you could probably dispense it with precision.
I remember reading about someone who used an extra large veternarian hypodermic syringe "device" to dispense bore butter into their revolver chambers.
I've also seen a CVA brass bore butter dispenser on eBay a long time ago that resembled a large brass syringe for dispensing it. It was probably a discontinued item because I never saw one listed or for sale anywhere else after that. It was about the size of a large cylindrical powder flask with a plunger on top, and it looked like it was heavy duty.