I have /usr on a separate partition.
You can either specify it as a separate partition during a clean install or you can move your existing /usr to a new partition on an existing install. I have done both.
I did the latter following this;
I make no representations to its correctness, but it worked for me, but of course ymmv.
edit - I did that on 13.37 and after I accidentally (!) deleted the /usr I did a clean install of 14.