No hotshoe as you say, but you could use the camera with pretty much any optically coupled strobe. This could be via fiber optics or via an EV-controller type setup like Ikelite uses. But one warning: adding an external strobe means an arm and a tray/handle, which brings the 'compact' camera right back up into the bulky category. My little Canon A520 is dwarfed by my tray, arm, and Ikelite DS50 which is one of the smaller strobes out there! Even if you go with a really small Sea-n-Sea integrated strobe/arm/tray type combo, it's still much larger than the camera.
I can't tell for sure from the pictures, but it looks like the housing has a standard metal plate on the bottom for mounting to tripods etc, which would be used to mount to a tray. You could just drill a little hole in the diffuser or for that matter probably just 'tape' the fiberoptic cable for a strobe to it, while covering the rest of the diffuser with black tape so you don't get the backscatter issue from the internal strobe right next to the lens. (If using an EV controller, just make sure the tape lets some side leakage out and it'll be picked up.)
I don't know about preflash, but assume that since the camera doesn't have a manual setting it is doing a preflash. You can get by without full manual, assuming you also have an 'exposure correction' option on either the aperture or timing priority mode. I'd for example in aperture priority set a reasonable aperture size between 5 - 7, and then turn the exposure compensation DOWN until you get a good darkish blue / black background in the water, then use the strobe power settings to control how much brightness you have of the near subject. Ditto in timing priority - set a reasonably quick exposure time that won't cause hand-shake focus issues like 1/125th or less, and dial down the exposure adjustment so it doesn't just go and open the aperture full on and give you too shallow a depth of field. Ditto with using the strobe for the actual subject lighting. You will want to figure out if you can do white balance 'manual settings' by shooting something white though, since the camera doesn't have RAW storage. But worst comes to worst you can set it for 'cloudy' which with an external strobe usually isn't that far off the mark, especially with a smaller strobe that's going to fade pretty quickly.
BTW, I'm a pure noob myself, so take all the above with a grain (block) of sea-salt!
