I am pretty much a novice on NW, but I did just get comped to gold status last month. So I can tell you what I learned.
They comped me to gold based on my platinum status on AA (which as you probably know is the equivalent of NW gold). So I assume they would be willing to do an AA gold to NW silver comp as well. They asked me for AA mileage statements for the past three to six months. I was able to print monthly statements off of aa.com that showed both my monthly activity and cumulative annual summary for 2003. You send this info with a cover letter to Emily Hayes at WorldPerks Customer Service Center, 601 Oak St., Chisholm, MN 55719-1995. Or you can fax her at 218-254-7567. Make sure to include your WorldPerks number.
The big question, in my mind, is whether they would comp you based on getting AA gold from one transpacific trip last year. On one level, it shouldn't matter to them how you earned your miles. But they may feel better about assuming that someone flying several trips a month for six months will continue to do that than they would about someone who did one transpacific trip. You might mention that you did three trans-ocean trips last year, on NW, DL and AA, and since it seems that similar trips will repeat this year, you might say that and explain why.
The thing I think you don't want to do is get so specific about the upcoming trips that it becomes clear to them that they are going to get your business whether or not they comp you. Your leverage is that you have a choice, but you like the NW, KL, DL, CO alliance because it gives you slightly more flexibility, but in the end, you want to fly on an airline with which you have status.
That, at least, would be my advice.
BTW, I made my request in late December and got NW's response on January 10, giving me gold through 2/28/05.
Hope this info helps. Good luck!!