If it were me, I'd go on the higher end of that 20-30 IBUs. Whatever .5 or .75 ounce to get you there for a 60 minute addition, then do a .25 or .5 ounce 5 minute addition. That way you get some aroma in it. that may only add another 2 IBUs, so no big deal.
With all of that DME and the sugar, what is your OG supposed to be? You are definitley going to need some hops to balance that--because I'd bet it is goign to be fairly high.
FWIW, Ray Daniels in Designing Great Beers suggests a .5 to .7 BU:GU ratio for brown ales. IMHO, you need to up the IBUs then.