SQL Server Replication across firewall
Are you able to set up a shared folder where only the SQL Service accounts have access? If so, since you are looking for a read-only subscriber, one option may be to use log shipping leaving the database in STANDBY. Of course, this is dependent on how often you need the data updated. Every time a log is restored, the users will be kicked off the secondary. Let's say every hour you restore a log backup, users will be kicked off during the restore, but the data will be pretty close to that time.