When wiring a digital dimmer (i.e. Maestro, Maestro RF, Spacer System, Radio Ra, Homeworks, etc.) in a 4-way circuit with two accessory dimmers, the question has come up: "How do you wire the dimmer in the 4-way location when that location has four wires, but the dimmer only has three screws."
You need to connect two wires to the blue screw. You would use one wire from each set of travelers. Typically the same color wires. The traveler wires you connect to the blue screw should be the same traveler wires that you connect to the blue screw on each dimmer in the other two locations. You can put one wire on the blue screw, and one wire stabbed into the hole in the back next to the screw. Another option is to connect both wires together, under a wire nut with a little jumper wire, and connect that jumper to the screw. The remaining two wires connect to the remaining two dimmer screws. One wire to the black screw, and one wire to the brass screw. It doesn't matter which remaining traveler goes to which remaining dimmer screw.