I used beNPC a while back and saved a Statesman costume (the manual typing in-game save that ends up in the data folder). I don't really know how to interpret things, but I've got a few items in the file that may be interesting. Chest Detail, Shoulders, Neck, and Back are all preceded by "none" in the various variable fields, which leads me to believe they are not where the cape is (compared to things like Pants and Chest which have "Statesman" type stuff in those fields).
However, there are two entries that do have stuff:
15,"Statesman","Statesman","none","Collar",-30388,-
17,"GEO_Capeharness_Statesman","none","none","Cape",-30388,-
The cape entry also has, unlike everything else, some words that follow a lot of numbers (everything else is just numbers until the next entry title):
17,"GEO_Capeharness_Statesman","none","none","Cape",-30388,-16769280,0,12499199, [a lot of zeroes cut for space in the post],"Capes\Hero\Statesman\Cape_Statesman.fx",16746828,7936,0,0
I just remembered: I was trying to make a Zombie Statesman (succeeded reasonably well) and couldn't get the cape through the normal costume creator. But beNPC has it, so you'll likely have to use the database editing trick if you want it on your own characters.