The smell is going to be the hard part... one of the better things to do is let the bass sit outside of its case, and leave the case open and exposed to fresh air for a really long time... it can take months. If you have an ionizer or air purifier in the same room, it'll help.
As far as a cleaner goes, this is the best stuff I've found...
http://www.stewmac.com/shop/Finishing_s ... olish.htmlYou'll probably have to clean it several times over the course of a few weeks... a lot of times that muck and funk gets integrated with the silicone from old polishes and there's a gummy residue on your finish.
That polish will slowly break it down over time, but is gentle enough to not kill your nitro.
I'm sure people might have other great suggestions and miracle cures, but... patience and a gentle silicone-free quality polish is what I've always used.