Replacing 3-way switch in 4-way circuit with an occupancy switch - not working correctly
You generally have 3 conductors in a 3/4-way switch loop, and you can't misuse ground as a conductor.    That leaves Only two ways to do it (short of a relay and low-voltage wiring): 

Smart switches in the auxiliary locations

Obtain smart switches designed to be "remotes" for the main motion sensor and interact with it electronically, either using 1 wire as a data line, or wireless via power-line signaling or radio.   

Very lucky topology

This can only work, if 


supply power comes in to the light, the switches are all one spur, and the motion sensor is in the first box.   
supply power comes into the same switch box as the spur to the light, and the sensor is in that box. 
the essential interconnections are in conduit, and you can pull more wires.  


Otherwise you'll have a spot where you need 4 wires, and you only have 3 in the walls.

Your sensor needs three wires coming in: always-hot, switched-hot from the switch, and neutral for the light's current return.  The sensor doesn't need neutral, but the light does, so inevitably neutral must come back this way.

http://www.lutron.com/TechnicalDocumentLibrary/369488.pdf

It does not support a 3-way switch.  It supports a plain switch which switches between 'open' and always-hot or switched-hot. If it is placed in one position and the one other position was a 3-way switch, then they have you rewire the 3-way to be a plain switch.   

Since you have two remaining positions with manual switches, those two positions must together emulate the behavior of a plain 1-way switch.   They way you do that is the classical 3-way circuit.  The 4-way switch needs to be swapped out for a 3-way.  Which you happen to have spare. However, if supply to the light also travels the switch wires, you'll need 4 wires in that segment: 


always-hot for the smart switch
messenger 1
messenger 2
neutral to return current from the light


This is one more than a traditional n-way, installed with the usual 14/3, and you can't retrofit a consuctor.

This does work if your topology is just right: the two remaining physical switches are on a spur.  In that case you won't need to carry lighting power (i.e. The neutral) between switches and you'll have enough wires.