I've read dry hopping can help in creating the perception of mouthfeel that makes the beer feel fuller without raising the final gravity. For a beer that light, maybe throw in a .5oz of aroma hops to the fermenter?
I suspect you could also by a pound of extract, boil it in about .7 gallons until you reach .5 gallons and than add the fresh wort(after cooling) to the beer to boost the nonfermentables.
In my light beers(bitters, hefeweizen's. Don't have a way to lager yet) I prime my beers with extract in place of sugar. this is a couple bucks more expensive but in my opinion it makes a superior light beer for two reasons: 1. It adds unfermentables to the brew, increasing my final gravity and mouthfeel, as well as giving the beer a kick ass head. 2. I notice that the beers I use dme to prime with half very tight, small carbonation bubbles that are more like champagne than the typical homebrew bubbles. Again, this is my opinion, others disagree. I carb most my beers with corn sugar and there's absolutely nothing wrong with that, I just feel dme is superior to prime with when making light beers. But that's just opinion/experiences. But I also, at this point, exclusively make ales.