an APEXi N1 with silencer (or N1 dual with dual silencers) will still probably be much louder than you'd like.
Enjuku carries a HKS "Hi-power" or something to that extent-- that looks stock and apparently sounds almost stock, as well. I'm considering that for the same reasons you should.
BOVs are relatively easy to find in subtler flavors, although I can't tell you exactly which brands to pick from.