After a bit of trial & error I was able to do a flash dump through CodeWarrior. The first few attempts failed, apparently because the target system (5020DS) wasn't in the expected state. Resetting to U-Boot seemed make the CodeWarrior flash software happy.
So what is the expected state & how can I force the target into that state when I don't have U-Boot? (e.g., initial board bring-up)