Finally I gave up on the online schlockware and went straight to Flexbuilder (which has been sitting unused on my desktop), and I thought "Surely this will do the trick."
Imagine the look of abject horror on my face when I found that the ActionScript editor could not do the equivalent of Control-Shift-F (for Java in Eclipse). In fact, the formatter built into Flexbuilder's ActionScript editor won't even do auto-indenting: You have to manually grab blocks of code and do the old shift-right/shift-left indent/outdent thing by hand, over and over and over again, throughout your code, until the little beads of blood begin to form on your forehead.
I'm left, alas, with half-solutions. But unfortunately, two or three or ten half-solutions don't add up to a solution. (How fortunate we would all be if it did.)