To start the process you would need to have some proficiency in magic. Perhaps expert level in several schools that would most likely be needed for the transformation, Restoration and Alteration maybe. Then there would be other steps that were actually covered in Oblivion, like transferring you soul, temporarily, into an in inanimate object(hourglass). The benefit would be aimed at magic focused characters of course, perhaps bonuses in magic schools and/or magicka pools, but a decrease in physical combat abilities.