Now I'm using this hacky way to do it directly on ESX hypervisor host:
1. Get VMID
VMID=$(vim-cmd vmsvc/getallvms | sed -n "s:^([0-9])\s${VM_NAME}\s.$:\1:p")
2. Unregister VM
vim-cmd vmsvc/unregister "${VMID}"
3. Update .vmx file to add/define "Virtual Serial Port"
echo "
serial0.fileName = "telnet://:7003"
serial0.fileType = "network"
serial0.present = "TRUE"
serial0.yieldOnMsrRead = "TRUE"
" >> /vmfs/volumes/datastore1/${VM_NAME}/${VM_NAME}.vmx
4. Register VM
vim-cmd solo/registervm /vmfs/volumes/datastore1/${VM_NAME}/${VM_NAME}.vmx