I'd be interested to know how to do this as well.
Problem is, ED probably "searches" for the oculus driver before searching for the SteamVR middleware.
SteamVR also searches for the oculus runtime.
So how do you hide the runtime from ED, but then expose it for SteamVR to find. It might need a "forceSteamvr" command line argument or something.
This would need to be coded by the devs.
Come to think of it, using SteamVR probably just loads the oculus driver anyway (inside the SteamVR wrapper) so the graphical issues might remain.