I live in Anchorage, and last fall I dreamed up a 170 mile mostly trail route, but it isn't perfect. Here's my plan: 40 miles on the resurrection pass trail, transition to the 30ish mile Russian River trail at Cooper Landing(though I've heard there are lots of bears and the trail is easy to lose), then mosey into and past Seward and down to Caines Head state recreation area, which is another handful of miles.
And then Back Again.
Maybe I'll stop by the icefields behind Exit Glacier for fun, too, and my scouting on google maps has made me realize the Russian River trail might put me close enough to bushwhack over to Lost Lake, as well.
Here's a link to most to it, minus the Seward/Caines Head end: http://tinyurl.com/27lbbfj
Anyway, that's the best I've got at this point. there are road portions, you have to go both ways, you have to travel through two small towns, and the bear-danger may be severe in parts. Oh, and on the way to Caines Head you have to deal with the tides.
Is it a perfect plan? No, but I think that's what I like about it.