Yes that design has been proposed before. The mass savings from using a tensile structure can make up for the slight loss of thrust efficiency. There was a somewhat plausible design in Avatar.

http://james-camerons-avatar.wikia.com/wiki/Interstellar_Veh...

That is extremely wasteful, in an environment where every drop of rocket fuel is precious.

Its possible that the exhaust could be made to disperse without losing much thrust - like a defocussed electron beam. Just so long as its cool enough when it hits the habitat. Which could have an aluminum-foil shield or some such...