From what I understand of your post you're looking for the part I posted a link to directly above your initial post. This rubber plug pushes into the hole in the underside of the strut and it has an internal thread, so when you screw into it the plug expands to stay in the hole. (Like a rawlplug for a wall, hence the name rawlnut)
Sorry if I've misunderstood you completely, if I have then just ignore me!
Watshot's solution seems great though, I might be tempted to attempt that on mine!