Hi!
I've pushed quite a bit of firmware related work to osmo-sdr.git, specifically the USB DFU bootloader and an example project that can be linked to the application partiiton and installed using dfu-util.
There's a README file in osmo-sdr/firmware/usb-dfu-project/ which should give some basic instructions.
I'm right now again seriously overworked, so no time for more explanations at this point, sorry.
Regards, Harald