So how does one "embed" reference libraries to the add-in?
You don't.
Alternative:
Instead of Early binding, use Late Binding.
Example code of Early Binding.
Here we set a reference to MS Word xx.xx Object Library.
Sub Sample()
Dim oWrd As Word.Application
Dim oDoc As Word.Document
Set oWrd = New Word.Application
Set oDoc = oWrd.Documents.Open("....")
'
'~~> Rest of the code
'
End Sub
Converting the above to Late Binding.
Here we do not set the reference but let the code bind to whatever version of MS Word is present in the destination pc.
Sub Sample()
Dim oWrd As Object
Dim oDoc As Object
Set oWrd = CreateObject("Word.Application")
Set oDoc = oWrd.Documents.Open("....")
'
'~~> Rest of the code
'
End Sub
Similarly you can change your code for MS-Excel as well.