I haven't looked into the USB remote control yet however the code for it is included in this port (kbd.c). CHDK's implementation of this feature is very basic, simply checking for a voltage applied across the USB power pins. Please test this and let me know
I've been asked to upload my code so I've attached it. This code produces the working 101b diskboot, however is rather buggy for 102c. As I've said before I was still getting to grips with CHDK when I did 102c so that code needs going over.
Instructions for setting up your development environment are in
this post.
EDIT: See first post for source code.