Some actually use rubber bushings, while others use a simple pencil eraser and others have 'punched' some rubber out of black rubber stoppers. Oh yeah... Some have simply built up a layer of black silicone rubber along the back wall of the trigger guard. Your only limitation is that of your imagination.
If you can't find black mechanical pencil erasers, use a black magic marker to color a regular eraser. If you use an eraser (black or pink), it WILL get hard and crack after a while (think about finding a forgotten about pencil

)and will probably need to be redone, but as easy as it is... No big deal.
If your P-11 is going to be used for personal defense, you definitely want the trigger stop to act as an Over-Travel stop that stops the trigger just AFTER the hammer falls, rather than it acting as a 'Staging' bumper that stops the trigger just before breaking, where you need an extra push to drop the hammer.
Why?? remember me writing that the rubber eraser will get hard with time?

and... While target shooters and hunters may stage triggers, self defense shooters don't