Ha Ha I found it. There is only one. Carnival Spirit does a 6 day May 5, 2010. Starts in Vancouver ends in Seattle. Here are the ports. It's pricey and I don't see the point when you could do a seven day for less money. But I did find.
Vancouver, British Columbia; Cruise Inside Passage; Juneau, Alaska; Skagway, Alaska; Ketchikan, Alaska; Seattle, Washington