Hi,
I do not know if this is a option for you, but you could use the following workaround. Add an environment variable e.b. MSVC in Settings->Environment and create two envar sets. In one set MSVC points to MSVC8 and in the other set to MSCV9. Now use this variable within the compiler executable configuration $(MSVC).
If you open properties of a CB project and select the tab you can choose the env-set and so you can use both compilers.