Yes Jason, I'm amazed you are already going after double run emulsions; I figure there's enough to keep me occupied with SR and SRADs for a long time.. If you had a labstand and clamp like this (please don't spend this much money though...), you could easily hold a cork and mount the needle in that.
Unfortunately those MedVet needles are sharp; I thought they were blunt for some reason. It seems that grinding them down shouldn't be a nuisance.
The silver plating shouldn't be a problem, as Joe said, and as long as you flush your hypodermic needles with hot water after use and allow to dry, I can't foresee any "gunk" being a problem. The only thing that's going through it is silver-nitrate & water. I doubt that hypo will get rid of it since it's metallic silver though, which has effectively "printed out".
I honestly can't think of a more simple solution than hypodermic needles with standardized sizes. It's not about uber-precision per se, but about having a specific orifice that gives you the right "ejection" qualities; powerful stream, good back pressure, accurate placement in kettle. They're cheap and I also think that if you have the right s.s. needle, you should be able to reuse it as long as you want... but IDK.
Ron, with a simple magnetic-stirrer, would you ideally want the stream of AgNO3 to go right into the most turbulent zone, near the stirrer?