Is it possible to limit BitTorrent Sync connections to a a specific network using the client software? Right now the closest I can come up with would be IP limitations imposed on each client using a firewall. This seems like it would work fine, except for if any client somehow ventures outside those firewall restrictions.
If you are using Linux, iptables has a match called "owner" where you can apply certain rules based off the UID or GID of the process sending the data.
This will run btsync as the user btsync and all packets from that process that are going to a restricted IP will be dropped.