Ethan,
I think you should feel comfortable with Hebrew Chapter 10 where it discusses the Holy Covenant.
This is the thing that Jesus Christ shed his blood for.
The reason he came to the earth to die.
It is through this means that anyone and everyone might benefit through his shed blood.
Then I would work in the scripture in Daniel Ch 11 about how this same Holy Covenant would be undermined.
The Christian temple would be profaned by a disgusting thing.
You should then work towards discussing the JW baptismal vows and compare them to Jesus Christ's commandment.
Make absolutely certain their are no other names in the vows.
When you see that "God's Spirit Directed Organization" is in the vows ask them what that is and if it means you are now making a vow to men.
If they deny that you are making vows to men show them this quote from page 109 of the Jehovah's Witness Proclaimers of God's Kingdom Book about how God's Spirit directed organization is organized.
jvchap.9p.109Jehovah’sWordKeepsMovingSpeedily(1976-1992)
the Governing Body observed: "It has proved beneficial to have a number of brothers taking counsel together to consider the interests of the Kingdom work
Now explain to them how you feel uncomfortable about the Holy Covenant being undermined.
As a clincher you could show them this quote from a 1955 Watchtower Magazine:
w557/1p.411ChristianBaptismfortheNewWorldSociety
A Christian, therefore, cannot be baptized in the name of the one actually doing the immersing or in the name of any man, nor in the name of any organization, but in the name of the Father, the Son and the holy spirit.
Ask them why they get baptized in the name of an organization when they at one time thought this was a reprehensible thing to do.
Help them understand that the holy covenant has been undermined.
In Christ
abe