After spending a long ninght working through the Arduino IDE compile options, I was able to add support for TI's USBlib, which is used as part of the boot loader trigger. I decided to emulate he Arduino Loenardo boot loader process. This board appears as a USB VCOM port and connecting to it at 1200 baud causes it to switch into USB DFU mode.

Once I get DFU flashing working from the IDE's I'll post an update to the board package and corresponding json index file.