It is possible (from Australia at least). Try booking a 'dummy' business class return fare, and a 'dummy' economy return fare, note and compare pricings. If happy, try making a proper one way booking in business, and a proper one way booking in economy, normally their web site prices the outward and return flights separately in any case. Have you tried a general flight booking web site, often fares that look too cheap for full business class are 'mixed fares', also try your local real travel agent, here in Aus I normally get better prices from the real agent compared to Etihad direct or flight websites.