I tried my Ti S1 and it was a little snug making the light stick out too far and keeping the tail from making contact where the magnet would aid in retention.My Ti Smini fit about the same.The use of an additional magnet or two might help the S1s magnet maintain purchase. In short it could work in a pinch but I would never trust the retention in any situation where the light could be lost it just doesn't sit deep enough in the headlamp socket.
You may be able to ream out or modify the light socket for use with the S1 but I think it would be pretty easy to ruin it in the process. I don't think the Smini would be suitable at all for this mod since it lacks a magnet.
