Oooo. Just noticed you said this model doesn't have an analog input. That may be the key difference between the DCR-HC20 and 30.
It may actually have the hardware for video input already but disabled in software. The tax on a DV camera in Europe was higher if the DV camera had analog input because it was then classed as a VCR. There used to be dongles you could buy that basically flipped the analog input enable flag in the firmware. This was a few years ago so no idea if it is still true today however.