[Plugin: Contact Form 7] How to insert my custom php in forms

I’m using a form with this code:

[email* your-email] &nbsp [submit “Invia”]

and everything is fine. But I’d want to use this php that I’m already using for a search box:

<input id=”s” class=”text-input” name=”s” type=”text” value=”email… (è in buone mani)” onblur=”if(this.value == ”) {this.value = ’email… (è in buone mani)’;}” onclick=”if(this.value == ’email… (è in buone mani)’) {this.value = ”;}” accesskey=”S” />

This because it allows me to have a different bar, a message inside that disappear when you click on it, and the chance to eliminate the “submit” button (you just have to push “send” on the keyboard).
My question is: where should I add my code to make it work with contact form 7?
Thank you.