Hi Wouter,
There is a version of USBDM that works with that board.
It should be possible to use the command line option of the stand-alone programmers or TCL scripts to program the two board. It would require the two boards to be programmed with different USB ids so the "unique-id" version of the firmware would be programmed to the board. You can then select the bdm with the -bdm=bdm_name option of the programmer.
Please see this page for information about the command line options of the programmer:
USBDM-Flash-Programmers: USBDM Flash Programmers
See this page for general information about the USBDM version for these boards:
USBDM: USBDM Kinetis Debugger and Programmer
bye