Is there a simple way that does not involve adding more end to end wires to make this a two way switching?
Honestly, smart switches are the way to do that.   I still don't understand why you want a switch on the PIR, however; it only disrupts its functionality.  

So I would straight-wire right through the leftmost switch so it is bypassed.  In the right switch box, put a smart-switch "master" and control the garage lights.  Then in the leftmost switch box, fit a smart-switch "remote" that controls the master in a 2-way configuration (note that this switch does not interrupt any wires, but taps hot and neutral). 


Use systems like Insteon that use powerline signaling or their own radio comms (Insteon uses both), and therefore don't fail if you change your WiFi password.  Though it is certainly OK if they also talk WiFi/phone etc. 


You have to be careful controlling lights with your phone.  Code requires certain lights to be controllable via a physical switch in the usual/expected locations; this is so guests can navigate your house, and "guests" includes first responders.  Fortunately these aren't any of those locations, so you don't care about that.   However, the second impact is to resale value.  Nobody wants to buy a house where they can't control the lights.  And the smart-aleck response of "install an app" is going to cost you $1000 on their offer, because they will assume you did this a lot, and they'll have to put $1000 into an electrician to make it all normal again.