That's only about an 1/8 off either side at the nut, even less further down. I doubt if exposing the truss rods would be an issue from a width standpoint. The depth of the rods in the Spoiler neck may be another thing. Mica the Wise will know.
Bearing in mind, I wouldn't do it... but speaking purely hypothetically -if someone asked me to do this and I couldn't talk them out of it- in order to do this cleanly/correctly, I would first de-fret the bass, then mark it *carefully* before reaching for a rasp, re-fretting afterward. Also, would need to address the string spacing at the nut, and possibly the bridge.
Or you could just send that big ol' wide-necked beauty to live with me and my 5-string Persuader... DOH!!! =)