you might be able to do that by hitting the restart button at half bar of the part before the part where u want to half bar fill( it still will be full bar fill, but since u cut the previous bar in half, in effect it works), good example try playing "Desperado" it works for me.
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Tye
SD9, Audya5, Genos, Roland XP60, 2 Yamaha DSR12, 2 Yamaha Sub, 2 Turbosound 2000