The ONTRAmail editor does allow you to specify that the email is From the "Contact Owner":
The Contact Owner must have a validated email address. You can see the validated email addresses in "Administration" > "Email" > "Email 'From' Address Setup". If their email address has not been validated then the Account Owner's validated email address is used.
The Raw HTML Email editor does not have this option listed and uses the word "Default" as the only variable, so we'll keep this feature request open. The "Default" email From address is set in "Administration" > "Email" > "Email From Address Setup" and is initially the Account Owner's validated email address. As stated in this request, that default email address will be used for all messages regardless of the Account Owner.