Title.
And how to do it if its posible

You can change an item.dat, add on you full 512 textures and then convert textures in bmp format and place them in your toricustom folder
Or you can just find somebody who has a full 512 and copy his item.dat file or even simply replace his textures with yours in bmp format according to names

Here's a tutorial that should explain it: http://forum.toribash.com/showthread.php?t=195093