Let me explain... (and no, an angle grinder won't do)

Based on the operation of my automated cat feeder (http://
www.newtonnet.co.uk/catfeeder) I've been asked to develop a similar
device for dispensing nuts to birds. The existing design will be
modified slightly to reduce the amount of nuts dispensed in any one
'serving' however its basic principle will remain the same: a motor
will slowly turn a paddle and provide six servings per revolution.

What I want to do is be able to do is trigger only a single serving
and, given the somewhat inexact method by which this paddle delivery
method operates, I have decided that my best bet is to somehow detect
the ejection of a bunch of nuts (there'll be less than 10 per serving
i.e. per section of the paddle) once they have left the dispenser.
This detection can then stop the motor turning and await the trigger
for another serving.

I've been experimenting with a break beam detector (a Velleman MK120
hobby-type kit consisting of an IR transmitter/receiver) and whilst
the detector functionally works and is great for detecting even a
finger quickly passing through the 'beam' I am not having quite so
much success with the smaller, and I guess faster, burst of nuts going
through. I have yet to try focussing the falling nuts via some waste
pipe or similar but I'm beginning to think even that might not help
much.

I was wondering if anyone here could think of an alternative, and
hopefully better, way of detecting what is essentially a small amount
of nuts falling out of the dispenser? Perhaps something like a gate
type arrangement attached to a lightweight microswitch that the nuts
fall through activating in the process...? I want to keep things
simple, not only to ensure reliability but also because the budget is
finite and there's a inevitable skillset limitation too!

Does all make sense? Any thoughts would be greatly appreciated and I'm
keeping my fingers crossed that there's a genius idea out there that
I've overlooked...

Mathew