While I don't know of any such script, I do know that cpanel has a remote access API accessible through perl and php. You may want to post a request in the Job forum to see if anyone could code it for you.
Yup, I think it's the best option using phpManager if you are a reseller and want to give your sales reps easy access to create new accounts/clients on their own. On your side, you can always check via the "phpManager Admin CP" the new clients added or your reseller "WHM " control panel to confirm the new clients.
Just configure phpManager with all the hosting plans that you want your people to sell and you are all done.