SQL Server log shipping: How to give SQL Agent the needed rights to remote share?

This is an old topic, and somehow I have not been able to find a clear answer.

Setup: Two stand alone SQL Servers. They have full network visibility to each other. They are NOT in a domain. There is NO domain available. (I am using SQL Server 2014, but this exact issue applies at least back to SQL 2005.)

Everything "works" ... the only piece missing is that the sql job that tries to copy the log backup fails with this error:

Error: Cannot open backup device '\\sql2\sqllogs\NORTHWND_20150209053800.trn'. 
Operating system error 5(Access is denied.).

SQL Agent is running as the "NT Service\SQLSERVERAGENT" account. On SQL2, I have given this user full rights to \sql2\sqllogs\ share and folder.

The SQLSERVERAGENT account on both systems has the same password, and the agent has been restarted after setting that password.

I have seen some folks solve this by making SQLSERVERAGENT a member of the administrators group on the OS, but that does not sound like a safe path.

What is the correct way to solve this?