I've considered putting automotive lights (LEDs perhaps)on the four corners of my bike and running it through an automotive flasher unit, with a switch and battery.

sounds like you've already got the switch and flasher. I don't see why you couldn't replace your broken light with a new one.

I suppose the reason I haven't gotten around to it yet is that I haven't felt all that much need for it. Hand signals get me through most everything.

But if you ride in heavier traffic than I do, then it might be worth your while.