Adding Using Code

You can use Application.SendKeys to add Watches
The VBE must be in focus when the code is run. You can either do this manually or use the VBIDE object to set the focus.
Call AddWatch sub with the specified arguments.
You can add these to a sub you call when you start a new session, as demonstrated in my "HelloNewSession()"

Enum enumWatchType 
    WatchExpression 
    BreakWhenTrue 
    BreakWhenChange 
End Enum 

Enum enumProceduresType 
    AllProcedures 
    Caller 
End Enum 

Enum enumModuleType 
    AllModules 
    CurrentModule 
    ThisWorkbook 
End Enum 

Public testVar As Boolean 
Sub HelloNewSession() 
    AddWatch "testVar = True", AllProcedures, CurrentModule, BreakWhenTrue 
    testVar = True 
End Sub 

Sub AddWatch( _ 
    expression As String, _ 
    Optional proceduresType As enumProceduresType = enumProceduresType.Caller, _ 
    Optional moduleType As enumModuleType = enumModuleType.CurrentModule, _ 
    Optional watchType As enumWatchType = enumWatchType.WatchExpression) 

    Dim i As Long 

    Application.SendKeys "%DA" 
    Application.SendKeys getEscapedSendkeysText(expression) 
    If proceduresType = enumProceduresType.AllProcedures Then 
        Application.SendKeys "%p" 
        For i = 1 To 1000 'You could use VBIDE to count the valid types to actually scroll up the right number of times!  
            Application.SendKeys "{UP}" 
        Next 
    End If 
    If moduleType = enumModuleType.AllModules Then 
        Application.SendKeys "%m" 
        For i = 1 To 1000 'You could use VBIDE to count the valid types to actually scroll up the right number of times!  
            Application.SendKeys "{UP}" 
        Next 
    ElseIf moduleType = enumModuleType.ThisWorkbook Then 
        Application.SendKeys "%m" 
        For i = 1 To 1000 'You could use VBIDE to count the valid types to actually scroll up the right number of times!  
            Application.SendKeys "{DOWN}" 
        Next 
    End If 
    Select Case watchType 
        Case enumWatchType.WatchExpression 
            Application.SendKeys "%w" 
        Case enumWatchType.BreakWhenTrue 
            Application.SendKeys "%t" 
        Case enumWatchType.BreakWhenChange 
            Application.SendKeys "%c" 
    End Select 

    Application.SendKeys "~" 
End Sub 

Function getEscapedSendkeysText(ByVal text As String) As String 
    Dim char As String, i As Long 
    Const chars As String = "~%+^()[]" 
    For i = 1 To Len(chars) 
        char = Mid$(chars, i, 1) 
        text = Replace(text, char, "{" & char & "}") 
    Next 
    getEscapedSendkeysText = text 
End Function