Assuming this is not a windup, and assuming it is about spraying Gulf-sized areas rather than poppy fields, I fear that you are way off track in envisaging Pawnee-style kit - 'spray arms' - being strapped to a 737. Furthermore, the prospect of flying a 737 at crop-spraying height over an oil-smoothed surface is not one which would appeal to me - or to cirr737's insurers! - it is inappropriate, and unnecessary.
The essential challenge (apart from keeping the CofG about right) is in securing a spray discharge with the right droplet size range. (Bear in mind that droplet formation is governed by the free surface energy characteristic of the liquid, and that that of a dispersant may differ from those of agri-fluids).
Overcome that, and Stokes' Law is your friend. You may achieve good and wide surface distribution from a sensible and safe height without spray arms, and indeed without any new penetrations of the pressure hull. ( If you are serious and need more 'gen feel free to PM me ).