[Plugin: Contact Form 7] Changing layout of checkboxes

Hi everyone,
I want to have a 12 item check box choice selection on my form. The only problem I have is that by default, the check boxes and labels appear one after the other, all scrambled together. How can I control the layout of the check boxes so that they appear 6 on the right and 6 on the left in two nicely organized columns?

The code I used to create my check boxes tag is:

<p>I am interested in<br />
[checkbox interests use_label_element "Cell phones" "Wireless Data cards" "VoIP" "Long Distance" "Data Networks" "Voice Services" "SIP trunking" "Routers and Switches" "Cloud Computing" "Hosted Applications" "Saving Money" "Interested in others"]</P>

thank you for your help in advance!
Rafa