[Espeefan]

I don't have any experience with MFUs but what I would do is find a relay switch and trigger it to close by wiring it to one of the outputs that the MFU uses to turn on it's own LEDs. Then whenever you turn on the lights controlled by the MFU, the relay will close and send power to the step lights. You could easily wire any extra LEDs to the same relay and their would be no limit to the number of LEDs you could add. The only limit would be the current capacity of the relay itself. Another option would be to control the relay switch with a free channel, if you have one.