You can use CrossStudio for ARM with a third party supplied ARM GCC toolchain. To do this you must set the environment option Tools > Options > Building > Use External GCC to Yes.
The location of the third part suppled ARM GCC toolchain is determined by the global macro ARMGCCDIR. To set this use the Project > Macros... dialog and specify the ARMGCCDIR value in the global macros editor. The prefix used by the ARM GCC toolchain is specified by the global macro ARMGCCPREFIX.
ARMGCCDIR=C:/Program Files (x86)/GNU Tools ARM Embedded/4.7 2012q4/bin ARMGCCPREFIX=arm-none-eabi-
When CrossStudio for ARM is started in this mode only "Externally Built Executable" project types are available. When you create an "Externally Built Executable" project you don't need to specify the location of the executable file. After the project has been created you can change the "Project Type" of the created project to be "Executable" and then add the source files to the project.
Note that no section placement or CrossWorks libraries are usable when CrossStudio for ARM is used in this way.