"I figured the parallel launch idea was more feasible than carrying anything in the bay, but I wasn't sure about the ability to get a Soyuz into the right orbit."

It can't. The easiest route for Soyuz to get a 28 inclination orbit, would be for Soyuz to loop around the moon. Now if Soyuz was launched from .07 at French Guiana that would be easy.:
"Evry, April 11, 2005 - Jean-Yves Le Gall, CEO of Arianespace, and Anatoli Perminov, Director General of the Russian space agency Roscosmos, signed today in Moscow the partnership contract concerning the production and supply of Russian equipment and systems for the construction of facilities needed to launch Soyuz from the Guiana Space Center (CSG) in French Guiana.

It provides for the manufacture, assembly and validation by Russian companies of Soyuz launcher interface systems and equipment, adaptation of this launcher to conditions at CSG (range safety, telemetry, environment), and completion of final development of the latest version of the launcher, Soyuz 2-1b."
http://www.arianespace.com/site/news/releases/05_4_11_release_index.html

I would guess these Soyuz are for satellite launches, rather than manned, but I suppose a manned Soyoz could be launched from Guiana, and NASA could buy from the French.

"Frankly, if we aren't willing to risk a Shuttle mission to Hubble, I'm not sure we have any business trying to get to the Moon or Mars."

I don't think the risk to the crew is significant, but with only 3 orbitor a Hubble repair is risking a orbitor, and losing another orbitor puts the Shuttle Program at risk. And having a back up Soyuz doesn't help in this regards. Of course you could forget the Shuttle and launch a Soyuz with crew from Guiana, then launch another rocket from Guiana, Sea Launch, or KSC with additional gear needed for Hubble repair. Think the crew would need to use Russia suits, though.