Changing obj file tree location

Hi

I've migrated to version 9.1, and wish to locate the "obj" directory into a different location - "OBJ_ROOT_DIR" as it appears in the makefile. How would I be able to set this in the GUI?

I've been able to set a different location for the ELF under "Nios II Application Properties".

I tried changing the "Build Location" under "C/C++ Build", however it misbehaved (a build would report "nothing to make", or if I moved the makefile the GUI wouldn't work when attempting to view properties).