I'll try to make a clear step by step later today or most likely tomorrow, but I think in that case the easier approach would be to first encrypt the whole drive during the installation step, and then resize the partition down to create enough space for your unencrypted space.
Although, I'm still a little confused because you mention that you can physically walk to your computers... wouldn't it be easier to just use another drive, like a USB thumb drive for that?
You can also setup a Samba or NFS server to share files over the network, even if they are physically close to each other. For reference: