How can I trigger an external flash for portraits with the HX-100V?

Hi pal, I have the same idea of yours and the flash holder as well as the syk-5 trigger were just arrived yesterday. I tried my YN-560 manual flash(I am a Chinese user, lol) on Slave 1 mode(using optical trigger on the flash) in door and the external flash works

Haven't got time to examine whether HX100 has a pre-flash which may distrupt the exposure of external flash yesterday, I'll try to test it out in the following days. Also I plan to order wireless radio trigger/transmitor for miltiple off-camera flash purpose outdoors(also for indoor event shooting since you never wish your external flash got triggered by flashes from other photographers). I'll share the result with guys here after I fully test out my gears.

Also big thanks for Dave's link as well as everyone here who share their thought on this issue.