When the control resizes, make it resize the form. Make the form use SetWindowRgn to restrict itself to occupy only the area covered by its menus. This removes the borders.

' Restrict the form so it just shows its menus.
Private Sub Form_Resize()
Dim rgn As Long
Dim wid As Single
Dim hgt As Single
Dim border_width As Single

    ' Create the region.
    wid = ScaleX(Width, vbTwips, vbPixels)
    hgt = ScaleY(Height, vbTwips, vbPixels)
    ScaleMode = vbPixels
    border_width = (wid - ScaleWidth) / 2
    rgn = CreateRectRgn( _
        border_width, border_width, _
        wid - border_width, _
        hgt - border_width - ScaleHeight - 1)

    ' Restrict the window to the region.
    SetWindowRgn hWnd, rgn, True
    DeleteObject rgn
End Sub