Don, I remembered today that I have two 58mm adapter rings for the cokin P system, very easy to put back to back with duck tape to make a reversing ring. I wish I had remembered I had these before spending all of £4.65
for the proper thing.
I have tried to take some photos with the 18-55 reversed on the end of the 75-300 but to get them focused is a nightmare.
I don't think I will be doing this very often. It took quite a while to find the right combination of the two lenses and then the maximum distance away was about 1".
I haven't given up as I have a canon 49mm to eos fit adapter so with duck tape I can now attach one of the 58mm adapter rings and just reverse the 18-55 and give that a go.
1st photo un-cropped
2nd photo cropped