I managed to do this. I am away from the machine with the code on it, but what I did is create a new emulator (I didn't use the existing Steam emulator). I did this because the existing emulator is geared toward running locally-stored games, and because it incorporates you entire library. I wanted streaming, and I also only wanted access to a hand-picked subset of games.
Anyhow, when you create a new emulator (I called mine Steam Stream) there is a parameter like "Command" or "Execute" or something... it's the command line that will be run when you try to launch something from this new emulator. The key is you want to specify this parameter to be
%PROGRAMFILES%/steam steam://rungameid/[NAME]
I created a folder containing a list of dummy TXT files, one each for every game I wanted available to stream. The files are named based on the Steam game ID number + ".txt". This is what I used as my "ROMS" folder for this emulator. The files themselves are empty. I just needed to point the new emulator to a list of games to work with. (Also, you need to specify in the new emulator that the extension for the emulator's ROMs will be "txt", or whatever you end up calling them.) Again, these aren't ROMs at all, it is just included because the new emulator expects it and builds the list of games from the folders contents.
Then you need to build a list of games, which I did by hand. Off top of head can't remember if this is a .cfg file or what. But it's the comma-delimited list of games that exists for each emulator. In the case of Steam streaming games, the first column will be the Steam game ID number, and the second will be the plain language name of the game.
I added all artwork using the same naming convention. So if a game had Steam ID 123456, the marquee would be 123456.png, for example.
You need to have the Steam client installed, of course. And you need to be on the same network as the Steam host.
Hope that clarifies. If not, when I get back to my other machine I can get more specific settings or screenshots.
This leads me to my whole reason for coming to the forum...
This set-up works great EXCEPT if your host is off, or is disconnected for some reason, it just hangs. I was hoping someone might have a suggestion about how to prevent users from trying to launch streaming games when the host is not available.
In my set-up, streaming games show up in their own Display. So I was hoping to just disable that Display if the host was unavailable. Alternatively, maybe there is an argument you can add to the Steam command line (above) that quits after failure to connect after X seconds or something.
