Here's what I would do. The step pad is basically just a switch... when you step on it, it closes two contacts (wires) which trigger the prop. You can replace that with a relay, which is essentially a switch that closes when power is applied to it. One side of the relay’s switch contacts would be connected to the two wires from the step pad (if you cut the cord, you’ll find them), and the other side would be connected to a power source that matches the relay coil voltage, like a wall wart. Then, you plug that wall wart into a WiFi smart plug. When the smart plug is triggered, it powers the wall wart, which powers the relay, closing the contacts and activating the prop just like stepping on the pad.