You need to be aware that the FET that acts as the switch for the AUX feature is only a 100ma rated transistor. The motor on the Mojo draws 189ma, so you are overloading the AUX switch circuit in your Foxpro by nearly double the amount that it was designed to handle. If you fry that circuit it is not covered by your Foxpro warranty.
Some guys are using the decoy and hoping that since they are not holding down the switch for long periods of time, they will be OK. Any time you overload the transistor you are creating more heat than it was designed to handle, thus reducing the life of it.
I emailed Foxpro about the possibility of using other decoys on their units and their reply was that the AUX jack was tested only with their Jack in the Box decoy and that the user should understand that if they used the AUX jack to control any other decoy, they were taking a risk of damaging their unit.
If you want to use the Mojo decoy with your Foxpro then you need to build a switching circuit to take the load off of the FET in your Foxpro or you will eventually burn out the circuit.
PS: If you decide to take the risk, your switch must be in the positive wire that goes to your battery. In other words, wire your 3.5mm cable into the + battery wire.