Ok, I found it out.
So here is how I did it, in case other people may want to know:
In the Properties of the project, under C/C++ Build -> MCU settings, I could see that the OCRAM section has the alias 'RAM3'. (here you also can change the sizes of the RAM sections)
Then in the code you can do:
#include <cr_section_macros.h>
__DATA(RAM3) uint16_t buffer[BUFSIZE];