The best way to fix this (in my opinion) Is to remove the fairing and fill the stripped holes with a high quality plastic weld / epoxy. Then redrill the holes out for the same screws. I have found that its best to drill a small (1/16") hole at the base of the screw boss perpendicular to the screw hole first. This allows the epoxy to get all the way down into the hole as the air can escape when putting the epoxy in.
Boy, it seems that lots of us have this problem...
Now that I've thought this through and have read the replies, we need to look at two different types of repairs.
1st fix type:
Temporarily tighten up a screw in the fairing as it's going back together. This can be done a number of ways listed above, wire in the hole, HDPE narrow strip into hole etc. This will get the fairing in place and hold it until the next time it's removed.
2nd fix type:
You're pulling the fairing off for something and you have time to plan and take the necessary steps to do a more permanent repair. If it's just a slightly stripped out hole like most of us seem to have, I would lean towards filling the hole with something that does not break, like hard epoxy might do. Something softer like the Bic pen dripped into the hole might make me happy, but getting anything to actually bond to the plastic is very hard to do. The best we can hope for is a mechanical bond or adhesion within the hole. The threads from the screw in the TPO (thermo plastic olefin) screw hole will work for the mechanical bonding.
IF YOU'RE DRILLING OUT THE HOLE AFTERWARDS, PLEASE TAKE CARE AND DO NOT OVER DRILL THE DEPTH.
I either use a short drill bit that can be sunk into the chuck so I only leave out the needed length, or I use a 1/4" socket that I slide the drill bit through and the drill bit adjusted to be just longer than the socket length and you cannot over drill the depth of the hole. Sometimes I still think I can use just enough force to drill something and booooom, it catches and comes out the other side, so be forewarned, do not over drillllllllll.
I'm not sure what HD has to offer, I did not look up the part number given above, but it sounds like they've had problems and came out with a repair for the stripped hole.
Thanks again to all the great comments and suggestions. I'm sure more will be coming soon.