All the answers to the original question are correct - thanks Henrik for spelling out the details better than the rest or us - you just have to choose the one that suits your style of thinking best!

To expand on my shift right and left, you would first write the high nibble, then shift left 4 times, then write the low nibble.
To recover you would shift right 4 times to get the high nibble, and to get the low nibble, shift left 4 times, then shift right 4 times. (Clear as mud?)
Basically, make the bits you don't want fall off the closest end, then make sure the ones you want are in the low nibble position.

Some other compilers have tools for directly accessing nibbles, but the need is pretty rare.