I just compiled a command line only version of Pico Drive for Diablo users. I can't test it since I don't have the hardware, but it should work.
In the attachment you'll find the executable file and a default configuration file. You should put them both in the same folder and execute picodrive from there. The configuration file is a standard text file you can edit to suit your needs.
Keys are configured according to the N900 keyboard scancodes. I don't know if these are compatible with older devices (I've been unable to find the N810's scancodes), so we'll probably need help here.