My plan for the missing PDC sensors is this.
As there is no mounting hole in the bumper at the moment and the sensor mounting point on the inside of the bumper is not there I'll need to fabricate something.
The sensor body is 22mm OD, I'll use a step drill to get a nice round 22mm hole in the bumper to start with.
The next part is to get a block of suitable material just big enough to hold the sensor securely and provide a secure pad on the bumper, use a 22mm holesaw to cut the retaining hole in the block.
Affix the block to the bumper with tiger seal, when all set, insert the sensor through the block and secure it in place, that way the sensor will be secure and I can adjust the position of the sensor until the face is flush with the surface of the bumper, it will look as OE as you'd get that way.
A pretty low-cost solution that should work fine.
Using something like this to fabricate small mounting block for the sensors.
lightweight , strong and easily worked , very bondable aswell.
Acetal block