Try this. Select your object and then the [M] icon.
In the Texture Editor select the Texture Source Editor by clicking the second button on the top of the selection box to the right of the TE frame.
This brings up the DTE.
You should now see what componants are active. With any luck you will be able to isolate the component channel you need by cancelling the channels you Don't need.

I'm not sure if this will work, but it's worth a try.
Hope this helps.

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