Yes, you are absolutely correct,

I think I spoke too soon. (Especially since I bought the SDK and a USB sniffer for just such a purpose!) There seems to be
quite a bit of data transferred back-and-forth to change even simple settings, which may be why it is possible to control the full usb device capacity of cameras with one machine. (128 cameras - #of hubs, I think.) This is why we're looking at PTP as a simpler subset of controls, which will hopefully support more than just Canons. It seems to be the approach that some other handheld remotes are taking.
I've browsed the devkitarm files for clues to how to make the GH lines an output with no luck. Obviously it can be done (
http://www.bayerdidget.com/Home), but whether this needs some bits of assembly code, I'm not sure. Memory.h is the key, I think.