I read last year that Boeing is working on growth versions of the Delta IV Heavy that factor in a substancial increase in throw weight by adding some strap-on solids. Without looking at the numbers and going from memory, I'm sure the upgraded Delta IV Heavy and the Atlas V Heavy would have sufficient lift capacity to handle the CEV.

The level of redundancy needed to "man-rate" the EELVs might not be as severe as you think. When they "man-rated" the Atlas for Mercury and the Titan II for Gemini, the state of rocket technology was very primitive by today's standards. Primarily, you'd need some additional monitoring to try and detect an anomaly in time for the crew to abort (something the Shuttle is very weak on). If they could man-rate the Atlas in 1962 and the Titan II a couple years later, I have to believe that doing the same to an EELV would be comparatively simple exercise. From the sounds of it, I suspect it'd take a lot less time and cost a lot less than developing "The Stick".

I also think it would be very worthwhile to have more than one booster capable of launching the CEV. I've seen what happens too many times when a launch failure grounds a vehicle (how many Shuttle flight has there been in the past 3 years?). There was one string of particularly bad luck back in 1985 and 1986 where every booster in the US inventory but the Scout was grounded.

- Titan 34 failure out of Vandenberg in the fall of 1985
- Shuttle Challenger failure in January 1986
- Delta II failure in the spring of 1986
- Atlas failure in the spring of 1986
- Titan 34 failure out of Vandenberg a few weeks later.

It got so bad at that point that I half-seriously suggested the need for launch escape systems for payloads.