Thinking about this over the week end, if my measurments are correct subject to wear i think the next size up is 7.5mm transferring to metric, so looking at the doors it appears the distance, door to hinge centre, to be able to drill is only 14mm, i guess a max size drill chuck would be 28mm then, it does concern me slightly as you only get one go to do it correctly, if you can find a chuck that small.
Heres another option to consider
http://www.ebay.co.uk/itm/Expanding-Adj ... Sw65FXtHpN by using in small increments i would imagine it possible to possibly do a better job than a drill. or this non adjustable one
https://www.ebay.co.uk/itm/7-5-8mm-Stra ... fvf9yjE7Qg in various sizes but probably a bit dear to be honest, first one i spotted.