I am sure there'll be a bunch of methods - given the fact that people are always on the lookout of virtualization nirvana and a quick google search brought me to the below blog
http://rhevdup.blogspot.in/2012/01/convert-vmware-esx-virtual-machine-to.html
You can basically see what optio works for you but techncially it's a questions you would find the best answers for in the KVM communities as there would already be a bunch of people who would have already tried it and would be well versed with the least painful process involved 