Anything works hand carving is a skill or you could clamp down a drill and shape a plug w/sandpaper lathes are good for quick precision work when you want to make multiples of the same plug they make quick work of it.
Cranky Old Bassturd.
I am scared of using plugs with screw eyes because there is always that fear they will come out with a big bluefish. I think if there was a way to develop a scew eye that expanded as you put it into the body of the plug it might work well. That would be pretty hard to engineer though. Your way or through wiring is definitely better engineered.
Toggle bolts, steve I think that is a good idea in concept but the design of toggles is such that the opening pieces are designed to open in an unencumbered empty space. I thought about what you suggested and they could work if you were willing to take the time and drill out a cavity in the unfinished plug by manipulating the drill at different angles whole keeping the pilot hole relatively small. This could make the cavity big enough to put the toggle in and manipulate it so that it opened and sat against the bottom of the wood. I also thought about how you would make the hook eye. I did find one that could work in theory here is a pic.
The ones in the top left or bottom middle could be used for the purpose you were talking about, with the added step of bending the hook into an eye after inserting the hook when everything is completed. It would have to be made much smaller than the ones I have used in construction. That would be such a pita though. So complicated. to do something like that, through drilling through the center, and using wire, just seems to be less complicated and would guarantee a better balanced plug. As they say balance is everything. Lots of guys out there making unbalanced plugs that don't swim right.
Maybe speedy madcaster or surfstix would have further feedback?