Вставьте это в модуль EnvironmentEvents в макросах Visual Studio:
Dim curWord As String
Private Sub TextDocumentKeyPressEvents_AfterKeyPress(ByVal Keypress As String, ByVal Selection As EnvDTE.TextSelection, ByVal InStatementCompletion As Boolean) Handles TextDocumentKeyPressEvents.AfterKeyPress
If (InStr("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_", Keypress)) Then
curWord = curWord + Keypress
If (curWord.Length > 2) Then
'AutoCompleteFromFile()
curWord = ""
DTE.ExecuteCommand("Edit.CompleteWord")
End If
Else
curWord = ""
End If
End Sub