Can you attach a USB-disk to a Linux VM that runs on ESXi ?
If you have no Linux-VM you can use any Linux-LiveCD.
When the USB-disk is connected to that Linux use sshfs in readonly mode and connect to the ESXi.
mkdir /esxi
sshfs root@esxihost:/ /esxi
cd /esxi/vmfs/volumes/datastore/vm/
dd if=vm-flat.vmdk of=20M | bzip2 -9f >/mnt/usb-disk/vm-flat.vmdk.bz2
When that is finished power off the Linux VM and send the USB-disk to the second ESXi.
Connect to the 2.ESXi via sshfs in write-mode and extract the bz2 archive to its new path.
This still uses network but that should be no problem as the traffic is inside the ESXi host only.
I use this approach quite often when I extract data from VMFS-volumes during a Recovery for example.
Converter would also work but it is less reliable and would hit the network harder.