Unfortunately, I cant. However, I was told that the form's code can be modified to accept any 3rd party email address.
What I was told that Namecheap have disabled sending any emails with the field 'FROM; containing email address on the domain that does not exist on their server.
It means our domain is registered through them and if we use email addresses that is not registered on their servers (Yahoo email address), it will be automatically blocked by them when the form tries to send a message. So any email that is not created on the CPanel will get blocked.
You may find this interesting. I am not adept on programming. Please see these:
Restrictions on the PHP mail function and sendmail use
http://community.namecheap.com/forums/viewtopic.php?f=16&t=1785
Sample PHP mail form
http://community.namecheap.com/forums/viewtopic.php?f=16&t=1876