To maneuver around this wall, Leverett suggested setting up joint intelligence commands for specific "targets."
This is essentially already happening. There are committes of experts from all the relevant agencies that meet and coordinate on a regular basis for all kinds of intelligence problems, especially strategic. My wife has served as her organization's representative on a couple of them dealing with nonproliferation topics. I've heard there are others (not sure if they're ad hoc or not) that work on more tactical problems or specific groups and even individuals. Even the UBL unit in the CIA CT center pre 9/11 might be an example, though perhaps not the best one. I don't know if any of these are formalized, however.