There are no boost specific settings in config.lua, since CEGUI does not use boost in any way, shape or form. The only reason you're having this issue at all is because Ogre exposes its boost dependency to client code - so here it's being dragged in in when building CEGUI, and later it will be your own apps that you build against Ogre that drag it in, too
As I understand it, there is a boost header that handles automatically determining which configuration of lib it thinks it needs and then brings it in for linking via those #pragma comment(lib, ...) type constructs (that I hate!). With this in mind, the project that is (indirectly) including boost's autolink header would need to be configured to link against the DLL c/c++ runtime (this should be how things are configured via premake for the dynamic CEGUI builds). For the static CEGUI builds, normally it will use the static c/c++ runtime unless STATIC_BUILD_WITH_DYNAMIC_DEPS is set to true - when that happens, it should again be using the dynamic c/c++ runtime. As far as I know (and I'm no expert) it is this c/c++ runtime setting that boost uses to determine which config of boost lib it will try to link with.
The default config is:WANT_STATIC_BUILD = falseSTATIC_BUILD_WITH_DYNAMIC_DEPS = false
This default setting is obviously is the config that gets used/tested the most and as far as I recall, nobody has reported the issue you're getting (so it's really hard to know what's going on with that).
As far as I know the only config that should cause the static boost to be brought in is:WANT_STATIC_BUILD = trueSTATIC_BUILD_WITH_DYNAMIC_DEPS = false
Now I have to ask a really silly question - if this is 'obvious' to you, no offence is intended
After editing the config.lua file, are you remembering to regenerate the solution and project files by re-running premake (i.e via one of the batch files)? And yes, this means you have to re-convert them every time - a real pita I know