The data connections shouldn't be *required* by a modern monitor, and Amigas can't read them on the RGB connector anyway. The main reason for a data connection is monitor->PC communication about monitor capabilities, the monitor gets all the information it needs about the picture from the sync signals.
I think there are a few diagrams on Aminet in hard/docs or hard/hacks which show how to make a simple connector, and a simple buffered one using a transistor, resistor and the +5V from the Amiga. I'll rummage around at home and see if I can find it...
