In the tighter places like Laura Cove (north end of Desolation Sound) simply anchor in the middle of the fairway and row the line ashore as eps suggested. Tie off and then return to your boat and take up the slack. When ready to depart simply slack the line, row ashore undo tie and recover the line. Most places in Desolation Sound you will be able to see where others have stern tied to trees as they show the use. Doesn't every boat cruise with at least one line 300 ft long?
A further suggestion to anchoring up in that area: use a trip line on your anchor. Those beautiful coves were commonly used for rafting logs and the bottoms often are littered with old cable and sunken logs. Squirrel Cove (for example) is one very beautiful spot with a very littered bottom.
Have a wonderful trip!