I don't have any schematic but you might take a variable resistor, and run resistors in order of bank, EG: Bank one connected to XX ohm, then bank two connected to XX+3 ohm, etc. As you would turn up the input voltage (Decreasing resistance from the variable), then it would allow more power to flow through the static resistors (the ones that look like little barrels with the lines), and finally get the LEDs to the threshold. If this sounds like a possible plan you'd want to try, I can go by radioshack and see what I can come up with to help you get such a setup going.
