I would really avoid tying onto the spinner arm for a number of reasons. One is that it's really going to mess up the action of how the whole spinner bait is going to work. It's not just that the spinner won't spin, but you'll lose the vibration, if the spinner is not spinning and is held in one place by the line, the spinner will act like a rudder and force the spinner bait to run not true or strait which will look unnatural..Also the drag of the trailing lure will probably make the spinner bait swim cocked out to the side. I've fished a lot of things with trailers, and probably the most effective and efficient way of tying in the trailer lure would be to tie to the bend of the hook of the leading lure.
The other concern with the trailer being tied to the spinner arm is that if you get a hit on the trailer only, that arm that you're tied to is going to put a lot of shock absorbtion into the system and make hook sets a little less sure.
Now you are right that catching fish on something you made yourself is a kick, you ought to try fly fishing, and tying your own flies.
Good luck,
Ron