My 2nd generation '96' Mitsubishi eclipse has the stock ground effects on it and the door caps are notorious for broken clip holders. I have a simple fix that is still holding up on my car at the moment.
supplies needed:
the proper clips that fit
40 or 80 grit sandpaper
Good duct tape
screwdriver flat or philips (to poke through the tape)

step one carefully remove the door cap if it hasnt fallen off yet.
there will be places where the clips used to be
use the sand paper to scuff upthe area around the clip holders clean off the dust to assure the duct tape will stick
tear off a piece of duct tape about 3-5 inches and poke a hole in the center of it
put the clip through the duct tape and mount the clip in the place where the holder was
tape it down and poke tear another piece of tape according to the size and poke a hole in it
lay that piece of tape diagonally on the clip and there is the simple fix.

after the and you are ready to reinstall the door cap the clips will not be totally sedentary so it will be a slight challenge to install the door cap.
line up the clips re-install the door caps.

for some added security
duct tape the door cap onto the bottom of the door real neatly.