@R**
, you should in theory be able to cancel your extension of stay on your ED visa and immediately apply for an extension based on employment. All the requirements are for that extension is you previously held a non-immigrant visa (of ANY type). and all you'd be doing is changing the reason for your extension.
Still I have seen many companies send people out to get Non-B's rather than try to coordinate pulling off canceling one extension based on education and immediately applying for a new one based on working.