It should be possible fairly easily by editing the 'contact' template. I can write a quick example if you like. That said, anyone interested in spamming you would completely ignore the message, which sort of beats the point. Are you using a CAPTCHA (be it Q&A captcha or reCAPTCHA) on the form? That's a good spam deterrent.
EDIT: Hah, ninja'd Brogan for once instead of the other way around. Yay me.