I use a Powershot S80 in manual exposure mode, slave flash is set to manual at the lowest power setting to save battery power. My external strobe is an Ikelite SS50 with TTL attached to a special trigger sensor that emulates TTL from strobe to subject. Slave strobe will not preflash so my dinosaur analog strobe can keep up and flash in time and with enough power when the shutter trips. The special strobe adapter is Digital Adapter 2 made by Heinrich Weinkamp purchased for $135 from Reef Photo in Florida.
As of CHDK release 1.2.0, I am now attempting to use the AUTO/Program/AV/TV exposure modes now that the manual flash setting can apply to all exposure modes. The 1st flash/image taken is wasted as the Digital Adapter learns how it should work. Subsequent shots after (if strobe is not powered off) will fire the external strobe at the correct time when the shutter trips.
My analog strobes are very old but still cost me new $400 for the SS50 and $700 for the SS300, the Digital Adapter for $135 allowed me to reuse them again with a digital camera. The CHDK Hack has made my UW Photography much more flexible and usable with my Powershot S80.
And of course I got RAW back since my Powershot S80 had it disabled by Canon designers.