sure you can, the exhaust manifold goes from 4 to 2 and then from 2 to 1 right? well, instead of going from 2 to 1, just do 2 all the way back.

this doesn;t apply for the turbo of course, since all four go to 1 then into the turbo. the turbo only has 1 outlet, so for a dual exhaust, you'd have to go from 1 to 2

however, if you got the $$$ you can twin turbo the I4, the outer tqo cylinders feeding one turbo, and the inner two feeding a second. with two turbos you have two outlets and thus a true dual exhaust. why anyone would want to do this I dunno.