The original proposal required that the undegraded digital representation of flagged content never appear on a bus (even the LCD driver bus) in the clear, specifically to thwart such an attack. (CRTs do not present the same kind of problem as LCDs because the video can be converted to analog before it ever leaves the final driver circuits. Of course, even if you could access the LCD driver bus you would be getting a decompressed and possibly otherwise manipulated version and not the original stream.)
Thus, there would be no clear text version of the signal "running around inside the box" to tap. You would have to probe the dies of the appropriate integrated circuits themselves. Although this is certainly not impossible, it requires more than a modicum of technical knowledge and also requires some specialized and rather expensive equipment. Anyone willing to go to those lengths would be better served by building an ATSC receiver from scratch.
This brings me back to my question: has the original approach been abandoned? If not, I'm having a hard time understanding some of the comments I've read that tend to minimize the impact of the broadcast flag implementation. The only explanation I can think of is that people have become so accustom to Macrovision, SCMS, and similar stupidity that they don't understand that this time it's for real...
The purpose of the broadcast flag (and all the associated DRM) is to protect the undegraded digital representation of flagged content. Your approach of creating a degraded analog rendition of the content does not defeat that intent. In fact, as of now, we will supposedly still be allowed to access the analog output of receivers, perhaps even at HD resolution. If a copy to analog and back is what the FCC (or anybody else) is considering a defeat of the broadcast flag then I'm afraid they have really missed the point.
Dan Lanciani ddl@danlan.*com