Ok, another idea.

Admittedly, this is not exactly a low tech solution, but…

One could use an fpv drone with a paint covered sponge duct taped to the front. Once the lens is covered in paint, you can either call the job done or go in closer without worrying about being seen by the camera.

You could use a can of spray paint instead, but then you need some kind of system to activate it, which complicates things.