If that was your experience - I’d make sure you’re taking in 1000 mg sodium (one full LMNT) per liter of water. You might want even more.
You could always go the route of the backpack on your back, but empty bottle on your frame with LMNT and carbs already in it that you could stop very briefly and top off with water at one of the intermediate aid stations on the way out and back. On the way out, I’m pretty sure that stop was at the top of Styles Brook Road before you make the turn up Jay Mountain Road about 1:10 in for me on a 6 hour pace. You might be able to get away with one bottle to that point, and an empty backpack with carbs and sodium powder already in it for that big climb up Styles Brook.
At the turn around, you could either have an extra bladder for your backpack and bottles already ready to go, or mix stuff up there. I’m forgetting where the aid stations were on the way back, Haven’t gone back to figure it out yet, but I think you could do a backpack back to the same aid station you stopped at on the way out at the top of styles brook and then top off there.