It's not generally a good idea to defeat that safety switch but the way the circuit works is this: when you are sitting in the seat or enough weight is placed in the seat, the switch is a closed circuit. If you have enough knowledge of DC electronics to figure out what that means, then I have said enough. The plug for the seat sensor is under your seat. One item of note, if you unplug the seat sensor, the engine will not start. There, now I gave you more than enough information that you should be able to figure out how the circuit works. If you decide to defeat the switch and something bad happens to you or your dog, I do not want to be blamed. Therefore, I am making the disclaimer that I did not tell you how to defeat it, I only told you how it works. What you do with that knowledge is on you.
Try lifting the seat up and then turn on the pto
Or if you do as above just add a bypass switch for when you need it and reset for normal operation.
Or a strap on sand bag.
Or dangle a dog treat over the seat?
On my tractor, all I have to do is put the "Range Shifter" in to neutral and I can stand up or get down off the tractor and the PTO will continue to run.