I think I just answered my own question. I've got the dock now - I gave the old m250 to my dad, and bought the dock for him (he's very happy, BTW, and my mom's envious of the dock/player combo - it's so small and she thinks the sound is very good for the size).
And the answer is - no the Clip was not built for the dock. The "compatible" connection for the dock connects to both the headphone and USB at the same time - fixed distance between them.
So the only way to use the Sansa Clip with the speaker dock, is to use it the same way you'd use any other MP3 player - by connecting to the mini-jack sound cable and jacking up the sound on the player.