Very delicate situation. If you have been given direct instruction to "train up" this guy you need to make sure you keep good faith with the company and do it. If you have been asked to help occassionally, I would find ways to keep myself out of the sight line of this guy. Make alot of busy work. Carry a clipboard/stack of papers and look worried alot. Give him only the specifics on the current project and a few of the particulars of the business as a whole. This person should only need to "acclimate", not learn the job.

For self-preservation keep a detailed log of your interaction with this person.