Or you could use a pipette (as mentioned) to keep putting drops on the end of one of the leaves. As the drops will merge, eventually it'll fall. Set up the camera on a tripod, point it at the leaf you want to shoot, make sure your hand will be out of (above) shot. fill the pipette with water and drop the water onto the top of the tip drop by drop. When you think it's about to go start shooting.
Ideally you'd need the camera in drive mode and with some sort of remote. May be difficult with the camera you have.
But you will have
very little time in between the drop falling and it going out of the photograph's frame. So rather than shoot when it falls, you'll have to predict when it falls. Hence when you think it's going to go, start shooting even if it doesn't.
It'll still take some trial and error and luck, but is possible...
Good luck!
Edit: or you could cheat even more, load the tip of the leaf with water with the pipette, then drop a drop behind the leaf. From the perspective of the shot, if you get it right, it'll look like it came off the leaf. A full-on cheat, but could work...