With a spray bottle? Would that work? Just spray and spray until it drips?
I'd probably do it a little differently, though. I'd lie my canvas flat, put some water droplets on it, add the pigment, and then tilt it so the droplets flowed down the canvas. I'd start with a few, keeping in mind you can always add more (and more liquid to the ones you already have if they're still damp) if needed.
If you don't have an eye dropper, you can get fairly good control with a straw.
Good luck however you decide to do it!