I took this trip last year and I couldn't agree more with the suggestion that you take the Western Express route and that your friend joins you from Cedar City to Blandon. That part of the trip is most stunning part of the whole trip.
But.....there's a couple things to think about.
Be realistic when you evaluate your & your friends fitness. It's likely to feel like a very full five days , 365 miles with some pretty big climbs thrown in and most often long spaces between stores or hotels. It's certainly possible, I did it in 5 days, but were times it was kind of tough.
And how your friend gets back home from Blanding is a interesting question. It's a pretty small town that's not close to a lot. If they can squeeze out another day they can ride into Cortez, Co. which would not be far off route for you and it has a small airport or a car could be rented there for a drive to a bigger city.
None of this is meant to discourage you, Just make sure you're both in shape and carry lots of water.