A suggestion from Quartz is to use the US Strategic Oil Reserve to target oil prices. I'm not so sure that Saudi Arabia is angry enough with Russia to go along with it, and I'm not so sure that the economics of it will work out.
http://qz.com/185137/obama-is-unleas...hould-use-oil/
Currently they're several thousands Ukrainian soldiers that are effectively being besieged in their bases on the Crimea. Eventually they'll need to be resupplied and it should be possible to do it with Ukraine's Air Force.