I don't think there is...
Your friend would have to use your account to update his copy of the game, but I believe you must have internet to update games.
You could get around that by putting the entire game, including the mod folders, onto a USB drive. I would reccomend at least a 4 gigabyte USB drive, because Sins itself takes up 2 gigabytes, and mod folders and such could add maybe .01 gigabyte.
Hypothetically, according to the liscense (pages 60 and 61 of the manual), you weren't supposed to give the software to your friend in the first place.
I quote:
"YOU MAY NOT Sublicence, rent, or lease the SOFTWARE or any portion of it."
No one seems to read the license anymore... except me.