I just downloaded Elemental Gimmick Gear for the Dreamcast from http://www.snesorama.us/board/showthread.php?t=12087, for which there are no mirrors. It's in bin/cue, which nullDC obviously can't load, so I tried to turn it in a self-booting CDI using Bin2Boot. Unfortunately, running it in nullDC only got me as far as the BIOS screen. I repeated the process just to make sure, and even used different versions of Bin2Boot, but to no avail.
The only other option left now is to turn it into a 'normal' (non-selfbooting) CDI (by using DiscJuggler for example) combined with an Utopia boot disc. But is that even possible in nullDC (running 2 discs?)