A B777's trim setting did not fall in the GREEN BAND prior to takeoff. After troubleshooting; a Stabilizer Trim computer system fault was discovered which was reset using an undocumented procedure.

Narrative

As we pushed back; we received final weights and I entered the ZFW and new CG on the appropriate FMC pages. As I reset the trim; I noticed that the trim setting was not in the green band range for takeoff. We delayed engine start (in the alley) and contacted Load Planning (LP). LP advised that the load was good/correct so we contacted Maintenance. We had no EICAS warnings or cautions and Maintenance advised they couldn't help us (this is not the nuisance warning described in the flight manual; though we did look at that as well). We called Dispatch and they were of no further help at that time. I advocated that perhaps if we began taxi; the nose strut sensor would make an adjustment to the green band rather than just tow back into the gate. By the way; the tow crew had difficulty with this non-standard push by now; not what they expect. We taxied out but the green band didn't adjust. After more contact with Dispatch and LP; we all agreed (Flight Deck and Dispatch) that we had to return to the gate to get this resolved. We taxied back and just before we turned into the alley; LP sent us an ACARS with a procedure citing a training and engineering document. The message stated they've been having some issues with the stab green band not extending when it should for completely unknown reasons. The procedure involved setting the CG to 44 and activating the V-speeds; then; setting the CG to our appropriate setting (38 in our case) and reactivating the V-speeds. The green band extended and the trim was now within the green band takeoff range. We burned 1000 lbs of gas and the better part of an hour getting to this point. The departure and flight were uneventful. Next day I called and spoke to the 777 Fleet Captain. He told me he was 'very uncomfortable' publishing anything about this 'fix' procedure because it's not supported by anything in the flight manual or by Boeing. The procedure provided by Load Planning referenced Company Training and Engineering. As far as we could tell; Maintenance and Dispatch were unaware of the issue until our event and we sent them the information via ACARS. The question at hand is; are we really just making the box do what it should; or are we masking some other issue?