Google's upload rate is going to be a hell of a lot faster than either of yours and more reliable.
Also, you'd rather not trust a company that hosts sensitive information for loads of companies but you're willing to set up a connection that's open for attack from anywhere on the internet over a home network with consumer grade equipment?
If you insist, the best way of doing this would be to set up a VPN connection on a host machine to allow access to the local network. I'd suggest doing this over Windows server and use SSTP if you're both using Windows to access the share. There's a load of info on how to setup VPNs using Windows Server's RAS roles. You can manage access using AD if you wish with Windows Server.
EDIT: In terms of real-time editing, he's not going to be able to edit off the share unless your upload bandwidth is at least on par with his download, So I don't really see why cloud options aren't viable, seeing as he'll need to download the files, edit them locally and then re-upload anyway.
W4terF0x reacted to Oshino Shinobu in Share HDD over internet?
