AppleTV Fast DD Method:

First make copies of the old appletv partitions that we care about (everythign except for the media partition)

This assumes /dev/disk2 is your appletv drive

dd if=/dev/disk2 of=partition.img bs=1024k count=100
dd if=/dev/disk2s1 of=EFI.img
dd if=/dev/disk2s2 of=os.img
dd if=/dev/disk2s3 of=OSBoot.img

Now lets put it back in place onto the new drive

dd if=partition.img of=/dev/disk2 bs=1024k count=100
dd if=EFI.img of=/dev/disk2s1
dd if=OS.img of=/dev/disk2s2 
dd if=OSBoot.img of=/dev/disk2s3 

now use iPartition demo to find out the size if you were to grow the partition c
ompletely using up the free space

then run:
gpt remove -i 4 /dev/disk2

then ummount the drives
then run:
gpt add -s 309849759 -i 4 /dev/disk2
where 309849759 = the # of blocks ipartition mentioned

then open diskutiltiy and format just the media partition (erase)