You can just remove the limitation in the linker file (Circle_App.ld) and extend the FLASH size up to 512KB.
Now, if you want to split your code into 2 subparts (debuggable and non-debuggable), you can take a look at CircleOS. Some functions are associated with the non_debuggable attribute to relocate them into a global section that will be relocated in the upper memory by the linker file.