This is actually pretty common – when my wife used to make it herself (before we moved near D.C. where pre-made injera’s easier to come by), she would cut it with self-rising flour. Much of the time, commercially-made injera (in the US) is cut with wheat and/or barley.
I am pretty sure that she never added yeast, but she did used to keep a starter in the fridge.
ETA: @thekaz, @anon67050589, I asked my wife about it, and she said here in the US, she always had to add self-rising flour. She could never get the bubbly-action using only teff. She suspects that only works in Ethiopia, where there’s something different in the air and/or water (conversely, cutting the teff over there doesn’t improve things, although some people do it). (This reinforces my suspicion that, in the US, there’s no such thing as gluten-free injera unless they import it.)
She does always use a starter. She suggests taking 1/2 or 1 cup of teff flour* (*edited for clarification), and mix that with enough water to make a paste so it’s a bit thinner than pancake batter – maybe like for crepes? Add a thin layer of water on top of this. Leave this out for three days or so.
ETA (again): But wait – there’s more!
The recipe was something like this: mix 2 cups of teff flour, 1/4 cup self-rising flour, all of your starter (as above) and enough water to make a thick paste. Let this sit for about half a day. Mix this with enough water so it’s thinner than pancake batter, and add a little bit more self-rising as you go. For best results use a blender as this also seems to help the bubbly-action.
