You should be able to remove the attribute presentation from the Editor and then people using the web or eclipse clients would not see the field. It would still exist in the underlying object but not on the editors that the normal individuals would use.
We've removed all of this from our work items, but I believe Estimate & Correction attributes are displayed in a single presentation line. You may have to look at how that is done and may be have your own presentation for just the Estimate attribute.
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