See Duncan's post on how to do this from the command line. The only options are using vim-cmd on the host, or using the Set-VMHostNetworkAdapter in PowerCLI.
vim-cmd
http://www.yellow-bricks.com/2008/12/08/enable-vmotion-from-the-command-line/
PowerCLI
get-vmhost hostname.domain.com | get-vmhostnetworkadapter -name vmk0 | Set-VMHostNetworkAdapter
-vmotionenabled $true