What is the best way to trigger wizard form submit?

I use the wizard form directive and the normal form has been divided to several steps.
What I wanted to do is when you click the second last **next** button (ATTENTION: not the last one),you can submit the whole data to the server side,and in the **finish step** (REALLY last step) you can show some messages returned from server side.But I didn't find a way of how.
So I just put a button in the **finish step** page and bind a click event to submit the data instead,but this is really not the way users desired.
Any ideas? thanks!