MWorks doesn't support multiple independent stimulus displays, nor does it support splitting a single logical stimulus display across multiple physical displays. The primary issue is that the refresh cycles of the two displays aren't synchronized, so it's not possible to efficiently render and present a single stimulus display frame that spans both physical displays.
There's more info in this discussion. The solution of using a Matrox DualHead2Go would probably work for your scenario, too. However, it's not clear that those devices are still being manufactured, as availability on Amazon seems scant. It's possible that another company makes something similar, but my brief search didn't uncover any.