Well prepared for means of restraining corporation (6)
I believe the answer is:
corset
'means of restraining corporation' is the definition.
(a corset can be used to restrain fat)
'well prepared' is the wordplay.
'well' becomes 'cor' (both can be expressions of surprise).
'prepared' becomes 'set' (set up or ready).
'cor'+'set'='CORSET'
'for' acts as a link.
(Other definitions for corset that I've seen before include "Stiffened undergarment" , "Sector (anag)" , "Restraining undergarment" , "Tight-fitting ladies' garment" , "Type of bodice" .)