You can make a wired remote shutter release quite easily from a 2.5mm audio plug and a couple of switches, a 5 minute project suitable anyone. After I built mine, found this diagram. (As i didn't initially have a diagram I just tested all 3 pairs until I found the correct one)

Before I added the switches, I just dropped the exposed ends of the wire into a glass of water for long exposure astro-photography. Just pull the wire out when the time is up!!!