[Hope]

Can just say

“I bear witness there is none worthy of worship but Allah?"   because one only worship God and there is no need to mention Muhammad 

Your friend says that a jew can pray in a mosque..is it true? If that is the case, they are submitting to Muhammad and praying to Allah..not Elohim or Yahweh.,

So far no one has suggested to omit the name of Muhammad.However there were some hardcore Christian who wanted to add the name of Jesus as well.Then they read declaration as follows 



“I bear witness there is none worthy of worship but Allah,and Muhammad is the Messenger of Allah.Isa ,son of Mary is also messenger of Allah “

Jews can pray in our mosque as we don’t have any images and images of Mary and Jesus.

During prophets Muhammad time, There was a Christian delegation who stayed in Medina mosque for three night abd four days.