If you use grain instead of DME, you should be fine. Regular 2 row pale malt will give you about 36 gravity points per pound per gallon, not taking into account efficiency. At 70% efficiency, 1/2 pound in 1/2 gallon (2 quarts) will give you about a 1.025 wort, which is just about right.
I would go ahead and do a little mini mash. Don't steep the grain in a bag, crush it and make a real mash in a pot on the stove. Maintain 150 F for at least 30 minutes and strain the runnings through a collander or something. Mash in with about 1 quart of water, then sparge with another quart for a total of 2 quarts for your starter. Then boil as usual. This will take you some extra time, but will work just fine.
Prosit!