I agree that Melodyne should work, but you can also use the TC Helicon software which is bundled with RB. By using the pitch tracking setting you can isolate the offending note and use a midi note to harmonize to. You then have various options for applying vibrato, or not.

You may also be able to get some use out of Gsnap, which is a free auto-tune plugin.

http://www.gvst.co.uk/gsnap.htm

Hope this helps.

ROG.