This is one of those things that are mostly completely possible but the problem is that we have a high number of camera models, many of which operate in very different ways compared to each other in this respect. Further, even cameras that on the outside seem to work just the same, appear to require different sort of ways to do this. The result is quite a bit of a developer hell that nobody likes to touch, especially since we don't have a full pool of capable, coordinated and eager testers for all supported cameras & subs.
As you've noticed, Microfunguy has added this for some cameras in SDM. There's a thread about it here, the link below points to my development test patch to enable this in a crude but perfectly operational way for CHDK Lua for a570 (the commands added by this patch may never be added to CHDK trunk because it's really one of those semi-dangerous developer thingies):
http://chdk.setepontos.com/index.php/topic,3228.msg30061.html#msg30061.
For any other camera... take a look at SDM source code I guess?