When you are in your iPad e-mail, click on the "Cc/Bcc, From:..." line. It will expand so you can press on the "From" line. If you already have your business e-mail linked to your iPad e-mail, that address will show up for you to select. Select it and it will fill in as the "From" address.
Note that this will NOT allow you to simply change the "From" line. You have to use an account that you've already linked to your iPad e-mail.
Hope this helped.
Marilyn