Just picked these up and they are perfect for using Rift.
The rimless frame and thin arms are great for fitting inside the headset. Very comfortable. And the lenses are nearly the same size as the Rift lenses, so I can get the full FOV while playing.
The model number is "Airlock Wisdom 203" if anyone wants to get them.
Where can I get that lense adapter? Is it available as a 3D printable file somewhere? Also, what Fielmann lenses or frame were you going to use? It seems similar to to this approach which uses 43mm zenni optical lenses: