What I've been doing lately is fermenting 6 gallon batches in 2 cornies, then transferring and combining them in the serving keg. It's been great. Just bend your liquid dip tubes on your fermenter cornies so there's about 1/2 gallon deadspace and you don't have to worry about trub pickup. Yeah, it's two vessels to clean, but they're really easy to clean and make sure they're sanitized.
This way, if there's any beer left over after transferring to the serving keg, I can use a couple grams of honey in a bottle and fill with a picnic tap/bottle wand and bottle condition what is left over. That's been really awesome too.