Haven't tried it, but everyone says if you are using lme to use maybe a 1/3 for the 60 minute boil with the hops, then add the rest at flame out. This is supposed to decrease the chances of scorching the lme, eliminate extract twang, and help with the color.
I guess dme can be adding anytime, but still recommended toward the end of boil.
Remember your hops do need to be boiled with some malt extract, so definitely add a certain portion to the boil, preferably dme if its in the recipe.
My next batch and am going to try this to eliminate the twang!