Expandable DDR2 SDRAM with AM3352

I am designing a board using AM3352 and using 64MB 16 bit DDR2 SD RAM presently. So it is utilising, A0-A12 address lines only for the moment. But I want to keep an option on the board for expanding the memory , like to 128MB as is done in Beaglebone or 256MB in EVM. In doing this , A13 , A14, A15 will also be required. 

So I am curious as to how should i provide for this option presently for 64MB keeping in mind the expansion. All the memories are in 84BGA , and for 64 MB there are more NC pins , so initially i thought routing those NC pins with 0ohm resistor in DNI or connecting directly A13, A14, A15 to the supposedly NC pins.

But now i have doubts over whether such arrangement is valid  and it will work or not . Please help me get rid of this confusion and suggest a solution. 

Thanks,