Dan
I have attached an HID-mouse/CDC composite binary for the FRDM-KL25Z. There is also a *.inf there for the CDC driver installation (the HID mouse part will immediatly start working since it doesn't need a specified driver).
The mouse is controlled by the accelerometer (tilt) and can be a bit of a nuisance when installing the driver (since it tends to run away) so it can be disabled by connecting the input PTA12 (J1-8 on the FRDM-KL25Z) to GND.
Once the CDC driver is installed a connection to it connects to a command line menu with various menus in it (hit the enter key in a terminal emulator to see the menu); in the USB sub-menu there is a command to move to USB<->UART bridging mode.
In the overview/statistics sub-menu the heap and stack usage shows that there is still about 10k RAM untouched so plenty of room for somewhat more.
Regards
Mark
P.S. I used the uTasker USB stack to configure this and could simulate the operation which saves needing to do any debug work on the real HW. Mixing HID and CDC proved to be quite simple (once the composite descriptors were entered correctly). The result works on all KL and K devices with USB since there is no HW dependency in the code above the HAL (hardware abstractation layer). I built the attached binary using a standalone GCC make file (simply load by mbed bootloader) but it also builds with IAR, Keil, Atollic, CW, KDS, Crossworks, CooCox (and the uTasker VisualStudio based Kinetis simulator).