There is a great book called,The Baby Whisperer. At 6 months, he is starting to learn that his actions do control mommy and daddy. I'm not saying that this is what is going on,but it is possible that he has learned (beause you guys have allowed it) that he gets to get out of bed if he cries at midnight. Maybe try comforting him,without picking him up....try rubbing his back,face,rub some Aveeno Calming Comfort Baby Lotion (lavender&vanilla scent) on his tummy and sweet baby face.
All of this done while sushing him quietly with some light relaxing music going. These things all worked for my babies. If I knew that my babies were truly hungry,then I would nurse them while I rocked with them....otherwise,I would just try the other soothing methods. It may take a few nights for this to work because he may get upset that he is not being picked up....be strong and do what your mommy instinct tells you to do. If you think that you just can't stand seeing him cry and you want to pick him up,then go for it....there will be other nights to work on the method. I know there were plenty of nights that I just wanted to hold my babies when they cried.
Good luck with your precious baby!!!
Tammy