sasha1 on "[Plugin: Contact Form 7] Contact form 7 with math captcha."

Hi, i want to add mathematical captcha in my contact form.
In default captcha which is quiz it can be only one mathematical question.
I want to display random numbers every time. I have done with javascript but it is not what i my client wants.
So can you guide me how i can achieve the mathematical captcha.

http://wordpress.org/extend/plugins/contact-form-7/