Best of luck with that. We are going the opposite direction starting a week on Monday, so I know of the hills you are describing... it won't be easy.
+1 to all above for suggesting that a diet at this point is too late. Better to haul your fat ass up those hills in a lower gear than try and pound up them. Just take it slow, maybe consider an extra cog or two on the back if you do not have gearing suitable for hills (e.g. 39 x 25 like me).