Different payment option problem

I have a form with paypal integrated. It's a registration form... and people can choose to click either 'pay by check' or 'pay online'... so, if they choose pay by check, and then submit, I want them to see a thank you page. Instead, what's happening is that they are forwarded to the paypal payment page. 

The form is here: http://newrenaissance.us/whats-happening/upcoming-events/the-fullness-of-time-conference/the-fullness-of-time-register/ 

How can I fix this?

The even greater problem is that we're not receiving the registration... because the system thinks the process has not been completed... since they didn't make an online payment.

Ahhhhh...excellent. It worked. I'd love to have that feature standard. I'm sure we'll have that scenerio come up often.