Sorry, we don't have any solution for oblique data in GE I-files. I was under the impression that most of the GE scanner software was upgraded to include DICOM support. If you can create DICOM files instead, then you would be able to transform your data fairly simply.
I'm not sure what information you have available to you. You might want to let us know, and then we can see if we can fashion another solution for you - transformation matrix, rotation angle, translation shifts. There is this link from several years ago that dealt with a similar problem, but cardinal datasets and registration techniques were the work-around.
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afni.nimh.nih.gov]