Instead of taking the most direct route up and over the biggest hills, have you tried zig-zagging it onto other streets so you take the elevation gain more in chunks? Yes, it makes the route longer, but it might actually make the commute more enjoyable.

I used to do this on my commute home in a previous job. If I took the most direct/shortest safe route between my office and home, it was only about 2.5 miles...but almost all of it was uphill--the upside was that getting to work in the morning was fast and took very little effort. Going home, I added about a mile to the distance using a combo of streets with more shallow grades and little climbs with bits of flat for "rest". It only took a few minutes longer, but it made me happier (and more likely) to bike commute.

There are enough Seattle TE'ers around here that if you need help finding alternate routes someone would probably have thoughts.