3 monitors - T500 and Dock

I have a ThinkPad T500 in a "ThinkPad Advanced Mini Dock".

I have 1 dell monitor connected to the VGA port on the dock.

I have 1 dell monitor connected to the DVI port on the dock.

I want to extend my Desktop to the ThinkPad screen and the 2 monitors at once. (3 monitors)

If the ThinkPad is closed in the dock, my 2 Dell monitor work.

If the ThinkPad is open in the dock, the ThinkPad screen works, and the DVI Dell monitor works. The VGA monitor has no signal.

How would I enable the VGA monitor to work when the laptop is open in the dock.

Thanks