I've got a test build for you, and a test lua script that you can test the timing with.
You have to start the script in continuous mode, or it won't work. The script immediately takes a shot and shows it on the screen. If it's out of focus, exposed wrong, or not what you want, press the shutter button again to exit the script, and try again.
Once you're satisfied with the first shot, which sets the exposure and focus, press <set> to start taking pictures. I think it will keep sync at 1000 msec per shot from the time you press set. Individual shots may be a little early or a little late, but they should average out and stay in sync.
You can play with changing the interval if you want. I tested it at 500 msec per shot, and it worked. It will get behind if the shutter time gets too long, and the shots may become irregular and lose sync.
A nice thing to know when you're setting the interval is that you can move the cursor left or right with the zoom lever. The left and right camera buttons change the number at the digit where the cursor is located.
Let me know how it works. Good luck.
Also, if you use the test build with other scripts, you'll see a lot of stuff printed about shoot keys pressed and such. It's part of my debugging process for the shot timing.
[edit]I modified the 2 attached files so they should stay in sync and show the precise shutter open to shutter open interval. Please download them again for your sync tests. Thanks!