Use Extra Light DME that has ppg ratings close to that of real 2-row, e.g. 37 ppg. I would recommend adding about half of it at flameout.
Be extremely accurate with your recipe; weights, volumes, gravity points contributed, evaporation from the boil, etc. (it may simply be a recipe issue). Employ full volume boils with no top off water whenever possible.
Don't add too much crystal. Keep it below 7% total.
Do substitute 10-13% corn sugar at flameout in place of extract. You'll need about double what is typically seen in all grain recipes. This technique works very well but is better in pale, low to moderate bodied American ales.
Make an appropriate sized yeast starter with high attenuating yeast. Intermittent shaking is good. Stir Starters are better. Yeast nutrient and/or amalyze enzyme may help.
As someone else mentioned, aerate well before pitching the yeast.
Keep your temperature control down pat for the duration of the yeast starter & primary. For instance, with Cali Ale yeast, consistent ambient air temps in the low 60s should work very well for you (if you don't have a thermometer to measure the wort/beer more accurately).
If all else fails, look into partial mash with some real 2-row in place of extract. Mash the grain around 147 F for an hour.
And lastly, patience. Give your beer 3-4 weeks before bottling.