Yes, you can do this from the ubiboot maintenance console that appears when you leave the usb cable connected when you boot. The network interface may not be installed properly - look for an 'Other device' called 'RNDIS'. You'll have to tell it to install a driver manually - I usually go with the 'USB Ethernet/RNDIS Gadget' by 'Acer Incorporated' as it's easy to find. Be warned - if you re-connect this device later on, you'll probably get a bluescreen, so uninstall it when you're finished.

Telnet to 192.168.2.15 (you'll have an IP on that interface already because ubiboot usefully starts a DHCP server). You can install the 'Telnet Client' windows component if you don't have one already. The MyDocs partition should pop up when it's booted, so you can copy your image over.

When you're in, cd to /mnt and create two directories, 'mmc' and 'sf'. mount /dev/mmcblk0p4 on sf and /dev/mmcblk0p1 on mmc. Then you can do the tar as you would have done on linux: