I have read many benefits received from tossing straw in a clay slip "dressing". Is it possible to get the same benefits from injecting the mixture into a bale?
To what end? Straw clay is nice and light, the slip keeps the straw from being a nice home for critters. If you came up with a way to inject slip into a bale, I imagine it would just end up rotting the bale out since the slip wouldn't be able to dry. Much better to just coat the bale with slip and plaster over it for protection.