Excel Custom Ribbon toggle button dependency

I'm trying to put together a custom menu, and I want 2 of the toggleButtons:"chkToggle1" and "chkToggle2" to exclude each other, meaning that when 1 is checked the other is not and vice versa.

            <checkBox id="chkToggle1" getLabel="onGetLabel" getScreentip="onGetScreentip"   getSupertip="onGetSupertip" getPressed="GetPressed" onAction="tgl_ClickAddin" />
            <checkBox id="chkToggle2" getLabel="onGetLabel" getScreentip="onGetScreentip"   getSupertip="onGetSupertip" getPressed="GetPressed" onAction="tgl_ClickAddin" />

Can you guys give any ideas on how I can do that? Ideally there should be a way to get the pressed value from another control by control.id without using global variables, but Google is not helping me, maybe you can.

In my XML for the workbook I've got:

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui" onLoad = "RibbonOnLoad">
    <ribbon>
        <tabs>
            <tab id="customTab" label="Contoso" insertAfterMso="TabHome">
                <group id="customGroup" label="Contoso Tools">
                    <checkBox id="chkToggle1" tag="chkToggle1" getLabel="onGetLabel" getScreentip="onGetScreentip" getSupertip="onGetSupertip" getPressed="GetPressed" onAction="tgl_ClickAddin" getEnabled="GetEnabled" />
                    <checkBox id="chkToggle2" tag="chkToggle2" getLabel="onGetLabel" getScreentip="onGetScreentip" getSupertip="onGetSupertip" getPressed="GetPressed" onAction="tgl_ClickAddin" getEnabled="GetEnabled" />
                </group>
            </tab>
        </tabs>
    </ribbon>
</customUI>

I've Added a Sheet to my workbook called RibbonReference (Which I'd recommend setting .Visible = xlSheetVeryHidden) and then added the following to a Module:

Option Explicit
Dim rib As IRibbonUI
Public ControlTag As String

Private Declare Function ShellExecute _
  Lib "shell32.dll" Alias "ShellExecuteA" ( _
  ByVal hWnd As Long, _
  ByVal Operation As String, _
  ByVal Filename As String, _
  Optional ByVal Parameters As String, _
  Optional ByVal Directory As String, _
  Optional ByVal WindowStyle As Long = vbMinimizedFocus _
  ) As Long

#If VBA7 Then
    Public Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (ByRef Destination As Any, ByRef Source As Any, ByVal Length As Long)
#Else
    Public Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (ByRef Destination As Any, ByRef Source As Any, ByVal Length As Long)
#End If
#If VBA7 Then
Function GetRibbon(ByVal lRibbonPointer As LongPtr) As Object
#Else
Function GetRibbon(ByVal lRibbonPointer As Long) As Object
#End If
        Dim objRibbon As Object
        CopyMemory objRibbon, lRibbonPointer, LenB(lRibbonPointer)
        Set GetRibbon = objRibbon
        Set objRibbon = Nothing
End Function
Public Sub RefreshRibbon()
    If rib Is Nothing Then
        Set rib = GetRibbon(ThisWorkbook.Sheets("RibbonReference").Cells(2, 1).Value)
    Else
        rib.Invalidate
    End If
End Sub
Sub RibbonOnLoad(ribbon As IRibbonUI)
    Set rib = ribbon
    Debug.Print "ribbon:-", ObjPtr(ribbon)
    ThisWorkbook.Sheets("RibbonReference").Cells(2, 1).Value = ObjPtr(ribbon)
End Sub
Sub GetEnabled(control As IRibbonControl, ByRef enabled)
    If control.Tag = ControlTag Or ControlTag = vbNullString Then
        enabled = True
    Else
        enabled = False
    End If
End Sub

'Callback for chkToggle1 getPressed
Sub GetPressed(control As IRibbonControl, ByRef returnedVal)
    If ControlTag = control.Tag Then
        returnedVal = True
    Else
        returnedVal = False
    End If
End Sub

'Callback for chkToggle1 onAction
Sub tgl_ClickAddin(control As IRibbonControl, pressed As Boolean)
    If ControlTag = control.Tag Then
        ControlTag = vbNullString
    Else
        ControlTag = control.Tag
    End If
    RefreshRibbon
End Sub
'Callback for chkToggle1 getLabel
Sub onGetLabel(control As IRibbonControl, ByRef returnedVal)
End Sub

'Callback for chkToggle1 getScreentip
Sub onGetScreentip(control As IRibbonControl, ByRef returnedVal)
End Sub

'Callback for chkToggle1 getSupertip
Sub onGetSupertip(control As IRibbonControl, ByRef returnedVal)
End Sub

Giving the result