Sorry to answer so late, Sean. You've probably headed out on the trip already.
You have a very ambitious plan. Making Shepherd Pass in a day with backpacking gear is tough, since you start below 6,000 elev, and climb to 12,000 feet. That will definitely put both your stamina and altitude tolerance to the test!
The time I tried that, we started the night before about 9 PM and climbed until midnight. Then continued all the next day to get to the pass. But that was years ago and we were carrying heavy packs with a week's rations.
As for transportation, click on the Orientation Notes above on the left, then search for "shuttle". There are a few numbers to call.
No matter what you do on this trip, I hope you will post a report. It is an epic adventure.