[Plugin: Contact Form 7] Textinput in Checkbox group

I need to have an “other” checkbox at the bottom of my checkbox group where people can add they’re own suggestions. So i will need to add a textinput after the last checkbox as shown below.

• Answer one
• Answer 2
• Answer 3
• Other

Textinput

Anyone has an idea how i can accomplish this?

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