Methods 1(if used before the PreRender event) and 2 should work in your case. Method 3 will not work, because the MOSS editor checks if its CssFiles collection is empty in the PreRender event and automatically adds the default css files (ms-rte styles) if the collection is empty.
I suggest that you open a support ticket and send us the code for your page so we can test it on our local MOSS server.
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