This is crude, but it's safe and effective:
I have a double layer of 7" plates on the outside and inside, back to back with the decorations sandwiched between them. Before putting them up I poked four holes in them, then fastened them together with nylon screws. I can attach toys to the screws if I want to. The cage as a whole is big enough that it doesn't look obnoxious, even though the plates look pretty big in the picture. The white marks that aren't screws are reflections from the camera flash.
The bottoms of the plates are a slightly larger diameter than the decorations, so if I wanted to I could cut the lip off the plates. But I like it the way it is - the extra width and height from the lip makes it basically impossible for anybirdy to get caught or cut their feet. There's enough clearance at the top for tiel safety too. I'll be on the lookout for some nicer plates or better still, some clear plastic discs that would work well, but the cage is useable for now.
Buster sat on the cage top and watched me install the plates, then volunteered to go inside the cage as soon as I was through. So there's no fear factor at all!