This would certainly work. Just remember that in order to use a dip tube you have to have tubing connected to the ball valve nipple in order to keep a siphon going.
The nipple screwed on the inside would not have to be tight in order for the siphon to work. I made a copper dip tube that screws into the ball valve in my keggle and I have to keep it unscrewed a bit to get it pointed down 90 degrees. I think that as long as it is screwed in by a few threads, there should be a good enough bond to keep the siphon once the water level fall below the valve coupling.