This sucks big time… 
Since it seems that you are an advanced user of Linux, I recommend the following:
a) Deploy vanilla Raspbian Jessie Lite
b) Setup your VPN tunnel on the Raspbian
c) Deploy Zulu (over VPN)
d) Deploy OH2 using apt-get (over VPN)
Optionally, you can deploy Zulu and OH2 manually:
OH2 snapshot
Zulu Embedded ARM 32bit HardFloat
(of course, you will need to download all of the above manually on your PC, using your VPN connection and then deploy on the Raspberry Pi)
I don’t use openHABian and I don’t know if you will be able to establish a VPN tunnel in advance of the installation steps…