There really isn't a way to do what you want to. You could simply buy a GPU that supports 3 or more monitors. You may be able to go into your BIOS and tell the mobo to not disable the on-board GPU (I doubt it), but you will still have the issue of conflicting GPU drivers (Nvidia and Intel). If you really want 3 monitors and minimal headaches, buy a card that supports that requirement. Good luck!