As a workaround, assuming the Mac version of StylePicker works similarly to Windows, you could create a "MyStyles.LS3" file in the BIAB file and see if that gets incorporated into the StylePicker.
Band-in-a-Box will load in all of the .LS3 files that are in the \bb folder (in alphabetical order), and append them to the StylePicker list.
Here is a link to more information about creating your own .LS3 files.
Just a thought. Don't know if it works for the Mac or not, but hopefully it does.