Hi Brad, it's not clear to me why you don't think you are meeting the requirements as is. Do the vehicles not qualify as low-emitting/fuel-efficient? The SSc4.3 credit language, for the U.S. version of LEED-NC, at least, only requires you provide these vehicles. It doesn't say you have to purchase them.
Let's take this conversation over to the forum on the LEED-NC SSc4.3 page, by the way, where there are more resources on how to meet this credit.