I have not tried it, but the Tirwal firmware (
(Perhaps) The best firmware for the HANLIN/BEBOOOK and OEM family again!) is supposed to add back support for MOBI DRM, i.e. make he MOBI PID available. However, I think you are better off stripping the DRM with mobidedrm.py. You will still need a PID to buy the DRMed ebook, but this can be from Windows MobiPocket Reader for example. In the US, stripping DRM for personal use from ebooks you bought is probably legal and certainly harms no one.