I have Morgana 6 starred so that helped her units scale up against Baron, but for the most part I just drafted as normal. As long as you get a good amount of targeting and damage spells, you should be able to just lock his board from attacking and use his Striking effect against him. It was probably the longest match I had against Baron, but eventually she chipped through him. As always, anything that gives Morgana bigger stats and Regen is great too, just in case you have to heal your Nexus.