what's the volume of the starter? if it's just 1L then pour it all in, no big deal. much more than 1L and I think the general consensus is to try and decant off as much of the starter beer as possible, but that's not necessarily because of the effect it has on your OG, it's more because starter beer is nasty and you don't want that to affect the final flavor.
I keep DME around just for starters, coz it's easy to calculate how much you need. If the mrmalty calculator says you need 1L, then you divide by 10 and that's how many kg of dme you need (100g for 1L, 150g for 1.5L 200g for 2L, etc).