You have to upgrade to SOLIDWORKS 2013 SP3.0 in order to have total control over the bend allowance for multibody sheet metal parts.
Note: Many thanks to Anna Wood for making me aware about this new functionality
While the ability to control the thickness, default radius and the bend allowance at the body level has been implemented in SolidWorks 2013 SP0, the workflow was not really intuitive for the user (read this article for more information about how this functionality worked in SolidWorks 2013 SP0, SP1 and SP2).
Starting with SolidWorks 2013 SP3.0, there is a new checkbox for the bend allowance at the body level that can control where the information is coming from: either from the Sheet Metal feature at the part level or from the one at the body level. Again, it is a good idea to rename your features accordingly.
There is still a little problem, this time with the way the sheet metal bodies with different K-factors are grouped in cut list items.
Watch this video to the end in order to see the problem and the workaround I found for it: