Guys,
I can't answer your question about how beneficial that extra crossover tube would be to a Duratec. However, I suggest that you take a look at this link for some great technical information on the Probe GT's KL V6 variable intake resonance system.
http://www.highlandsun.com/hyc/sae920677/ Adding a tube as described by Chris Hightower might work but there is clearly a lot of fluid dynamics to understand and fool around with to get good results. At best, just adding a tube would be a shot in the dark. There are whole groups of engineers at Ford devoted to analyzing this kind of quandry.
-Kurt
