Any flat surface will do and some little offcuts of 3mm hardboard as shims. Just find the high spot and press the drill down using one layer of shim at each end. Of course, it depends where the bend is located. If it is near the plain shank, you could hold the shank in the lathe and use the toolpost to push the bend using a soft pusher like a piece of wood. Great patience is needed and you will have to go just past the straight and come back to settle the metal down. If you can use the lathe, make a note of how far you moved the drill and also the ammount of bend still left in and you can reach the yield point without going too far past.
If I was using a long series drill, I would use shorter drills first to get the hole as deep as possible before finishing with the long one.