Guard trimming question

I've realised recently that the tyre scrubbing on my Jim is worse than I thought and am considering the full trim, as per the guide in the "How to" section. I'm cool with the instructions but I'm wondering how people who've retained the factory bumpers have solved the issue of the bumper corners flopping around due to not having a fixing point to the guards. I don't want to just glue them but also would like to keep any fixings invisible if possible.

Thanks in advance for your suggestions.

i what to no how people have done this to