I tried ewavr's DNG WB code on trunk 665 running on my a570is 1.00e (digic III, propset 2, vxworks). I shot to DNG in various wb settings (auto, manual, daylight and bulb) in P and M modes and a couple of ISO modes and opened them in gimp 2.6.1-1ubuntu3.
Compared to JPEGs, the colors are not exactly the same but they are certainly very close. From this quick test I'd say it works quite perfectly!