http://www.overcomingbias.com/2009/01/moral-uncertainty-towards-a-solution.html
Will Crouch is currently writing his PhD thesis on this subject. Also see the section on moral uncertainty here, where I link to Bostrom's old post and this talk by Sepielli.
http://www.overcomingbias.com/2009/01/moral-uncertainty-towards-a-solution.html