On a full-ish -300, it would seem a very good way to induce a rather large fuel imbalance before takeoff, 'cos you're going to be running that operating engine at some VERY high revs to keep that baby moving.
It would also make for some 'interesting' turns into the operating engine, especially at places like JFK, one of the worst offending airfields in the EK network for long pre-departure taxi times. (Seriously, is there anyone out there who's so 'company minded' that he'd actually try taxiing out at JFK one one engine? If there is, all I can say is - Yikes!!)
Stand by for the reports of baggage containers and ground staff sent flying all over the airfield by jet blast.
I seem to recall some US airlines trying this procedure on their 3 holers back in the first 'fuel crisis' in the 70s - until someone (inevitably) forgot to light up the third engine before attempting to takeoff.