You shouldn't need any additive with the No-Spin, it works on a different priciple from a Positrac. The additive for Posi rears is actually a friction modifier, necessary to allow the clutch packs to grab. Think of the clutches in a Posi like the clutch packs in an automatic trans, frictions and steels. Now a No-Spin is actually a ratchet mechanism, no plates or friction materials involved.
Use the same lube recommended in the manual. BTW, most performance gear lubes do already have the limited slip additive in them.
