The API docs (Chuck Petzold's book was my reference) would seem to
suggest running a SendMessage() call before and after the existing
SendMessage call to turn on and turn off the VK_CONTROL key when
applicable. This doesn't seem to work and I can't find any
existing/working examples.

Here is the most basic version of the code used to send the plaintext
(contractual obligations keep me from posting my exact code):

Private Sub SendText()
    Static working As Boolean

    Dim pressedKey As String
    Dim pressedKeys As String
    Dim scnCode As Long

    Dim interCharDelay As Long

    If (working) Or (pHwnd < 1) Then
        Exit Sub
    End If

    working = True

    interCharDelay = 5

    '// each "line" of text must have a CR-only at the end
    pressedKeys = Me.Text1.Text
    me.Text1.Text = ""
    call LogLastLine(pressedKeys)
    pressedKeys = Replace$(pressedKeys, vbCrLf, vbCr)
    pressedKeys = Replace$(pressedKeys, vbLf, vbCr)
    pressedKeys = Replace$(pressedKeys, vbTab, Space$(4))
    pressedKeys = Replace$(pressedKeys, "{tab}", Space$(4))
    '// follow lines should be changed to allow other special chars
    'pressedKeys = Replace$(pressedKeys, "{tab}", Space$(4))
    'pressedKeys = Replace$(pressedKeys, "{tab}", Space$(4))
    'pressedKeys = Replace$(pressedKeys, "{tab}", Space$(4))
    'pressedKeys = Replace$(pressedKeys, "{tab}", Space$(4))
    If (Right$(pressedKeys, 1) <> vbCr) Then
        pressedKeys = pressedKeys & vbCr
    End If

    Dim r As Long
    Dim x As Long

    For r = 1 To Len(pressedKeys)

        pressedKey = Mid$(pressedKeys, r, 1)

        scnCode = GetScan(pressedKey)'// function returns hw scancode

        x = SendMessage(pHwnd, WM_CHAR, Asc(pressedKey), scnCode)

        Sleep interCharDelay

        If pUnloading Then
            Exit For
        End If

        DoEvents

    Next r

    working = False

End Sub