How about building the eyes with "roll around" pupils, on a very slightly curved (upward on outer ends, down in center) clear retainer bar inside a clear "envelope"?
That way as you shift back and forth, the eyes "move".
FWIW, I have two EL panels (green) nearly the size of a regular sheet of paper, saved a couple decades back out of some ancient grayscale LCD panels (cant' remember what they were from). If I can remember where the other one is (one is in the next room), I could see about working out an inverter to drive it and making something like this. I probably won't get around to it, unfortunately. :/
In my case, to do the same thing, it would go on the back of the actual bike or trike seat, because my own back isn't visible.