1. Iterate through their default outfit and assume that is what they are wearing, but a quick check of Hadvar's inventory showed that there was not a list of armors but instead an entire set in there. This might make it more difficult but i hope not.
2. Create a gigantic list of every armor type and loop through it, calling Armor.GetArmorRating() Except that function doesn't exist to the best of my knowledge so I would have to write, in the script, the armor values for every piece of armor in addition to compiling the gigantic list of armor pieces. This is probably the worst option unless #3 turns out to be more difficult.
3. Make my own mod that doesn't use scripts and instead tries to modify a bow to look more like throwing knives.
I must say that what you can do with the built in papyrus functions is pretty insufficient for lots of things and that the kit in general appears to be a pretty poor design too (architecture, control, etc.). What other solutions exist? I'm really down for anything no matter how technically difficult; I only fear the tedious list appending in #2.