I came up with this idea a couple of years ago when the kiddos were smaller. Instead of dangerous metal ornament hangers, use twist ties instead. I don't know that's is necessarily safer if a kid was to ingest one per se, but it's a lot harder to get an ornament off when you twist tie it onto the Christmas tree. At first I used whatever random twist ties we had around the kitchen junk drawer. Then I realized that the plethora of clear plastic covered twist ties that take forever to remove from your kids toys could be used instead (they're a bit nicer looking than the ones that come in boxes of trash bags or on bread). They're usually quite large too so you could cut them (all you need is a regular pair of scissors) and get a few from one twist tie.
Another option would be to use some pretty, thin ribbon
(you could get all fancy with coordinating colors or something). But that costs far more than free stuff you were probably going to throw out anyway.