Walter, basically what Dorothy suggests for Jeux deau is "walking" the hand across the keys to prevent the extension. Basically, she says sink the weight into one note, then move to the next and so on and so forth, don't try to maintain the extended hand position. Which is dandy, except for the weight part, the video is available as a free sample on the Taubman website I believe.
In my opinion, from a musical standpoint, sinking the weight of the arm into every freakin note, is not only a waste of effort, it produces an articulated sound, and by sinking weight, I don't mean transferring weight. In the video, she clearly "lifts" and puts it back down again. Which, in my opinion works against the musical goals of the piece. It's kind of by definition a "weightless" piece.
Now, I'm a firm advocate of weight playing, but from a musical standpoint, I don't think the kind of weight playing that she advocates here serves a musical goal. It's just technically convenient. However, imo, there are much better solutions, that serve both ends.
Here's how I do it, the beginning at least. So, since the goal (in my mind) is a watery, weightless sound, I think the piece should be done without much weight, I control the sound mostly gesturally in this piece. I start, with a slightly higher wrist position to keep myself from using too much weight, and I also tip my pelvis back, to keep myself farther away. This prevents too much arm or back weight from getting in the way... IMO. Now, from this position, I can still be relaxed. Also, you need a loose wrist. So I start with a slightly extended hand position, but I'm not extending it fully. Play the first note, and as I play to the last note in the group of notes ie the highest, I'm grouping gesturally here. The hand closes simultaneously to prevent tension.
IMO, this solves both the technical issues, and the musical quite well. I can post a video demonstrating both methods if this helps anyone.