While adding cogs to a journal recently, I thought about this issue. Cogs are often quite "open" in structure and getting enough adhesive onto the thin metal struts can be a real problem. I tried adding a matching cardstock shape behind the metal embellishment and had a very successful result, especially when the item, like the cogs, could have a brad inserted as well.
The cardstock allowed a larger, non-perforated area of adhesion to be applied to the project and at the same time hid the prongs of the brad very efficiently. I videoed the process, view here or on You Tube...
Dixx