Tested on the S3IS, A540 (CHDK beta build), A570, A720
If you stack (around five is a good number) photos, you can virtually eliminate noise - by stacking them in PS. This script will take as many repeating shots as you want, bracketing the currently selected LEFT/RIGHT action by as many steps as you select. In Manual Mode, that'll be for Shutter Speed - but you could use it in any mode, as long as you had 'Exposure adjustment' in focus on the screen.
Script Code (save as "hdr-stack.bas" to your /SCRIPTS/ folder)
@title M Mode HDR Stack @param a Number of steps @default a 2 @param b Step size (1/3EV) @default b 3 @param c Number of Shots @default c 5 if a<1 then let a=2 if b<1 then let b=3 if c<1 then let c=1 sleep 1000 print "Preparing..." for n=1 to a*b click "left" next n for s=1 to a*2 print "Shoot", s, "of", a*2+1 for r=1 to c shoot next r for n=1 to b click "right" next n next s print "Shoot", a*2+1, "of", a*2+1 for r=1 to c shoot next r print "Finalizing..." for n=1 to a*b click "left" next n end