Anyway, back to the original question, luc, you'll need to get a flash bracket (~$10++ - $30) to mount the flash.
If the flash uses a standard PC cord, you could just mount it on the bracket and sync with the PC cord.
If the flash doesn't use a standard PC cord but can be hotshoe triggerred, you could get an additional "hotshoe with PC cord" (~$12).
Anyway, for the flash, the trigger voltage should not be more than 16V (according to Casio tech support).
Some cheap flash: Achiever 260T ($35, recommended by Alan Photo) has a trigger voltage of over 200V, so don't get it. Achiever TZ250 ($41) has a lower trigger voltage of 8V and I've tested it working with my QV2900UX. It's not very powerful (GN 83ft) but would already be much more powerful than the built-in flash (~GN 27 ft). It comes with a PC cord too.
http://www.achiever-hk.com/flash/dedicate.html
Achiever 630AF ($97) would probably work well too but I did not test it myself. I expect the voltage to fall within range.
http://www.achiever-hk.com/flash/auto.html
Any other auto flash (which allows you to set Aperture and ISO) would work too. If you want to check out the trigger voltage, you can refer to this:
http://www.botzilla.com/photo/strobeVolts.html