I would like to bring to your notice that under Section 191 of Indian Succession Act gifts in contemplation of Death (Donatio Mortis Causa) can only be given for moveable properties. Also such property must be specific one. You may further note that such property can also be taken back by the giver, who had given the same due to illness and was expecting to die, in case he recovers from his illness.
In your case you are willing to give your nephew a house, which is an immovable property. Therefore, such gift is complusorily registerable under section 17 (a) of the Registration Act. In my opinion you cannot gift such house in comtemplation of death.