Hi Brad,
If you don't mind doing a bit of destruction, this is how I do it.
1. Buy a special 3M tape (you can normally find it in motor accessory/spare part shop), it is like super glue
2. Remove fabric from both old speaker frets (simply cut and tear it off)
3. Cut the tape in small pieces and put them on one side(the side you attach to Beolab), remember all four corners must have tapes, then you can put some more evenly on the rest for the better result.
4. Put tapes on Metal frets' four corner.
4. Put the old fret back to Beolab, apply some pressure on the place you have tapes and leave it along for a while (this is recommended but I never do)
5. Now you can put both metal frets on top of old frets, again, you need to apply some pressure on the place you have tapes
I took one of the fret down and took some photos, I can send them to you if that will help, I had tried to upload but I gave up.
James