I am lazy, and I only make lures for myself and a few friends, so I can be less exact and it's still fine.
Since I can only do one spinnerbait at a time, I skip the fluid bed with spinnerbaits. I put the powder jar on top of a big piece of plastic baggie, heat the head, hold it with a pair of small needle nose vicegrips over the jar, and use my fingers to grab a pinch of power and drop in to the head. Since I'm holding the head over the jar, the majority of the excess falls back into the jar, and I use a putty knife to put the excess on the plastic back into the jar when I'm done.
If I'm doing a two color head, I put both powder jars on the same piece of plastic, spaced apart, and I can just reheat the head after the first color and do the second.
I find that I have plenty of control if the amount of powder and where it falls using my fingers. But I am no artist, and that helps.
I actually have more trouble curing the spinnerbaits in my toaster oven. It is always an awkward arrangement at best, keeping the hook and wire away from the heating elements.
My next project is to make a wire jig to hold them better.