Still a problem: it does not work, and by looking at the generated Makefile the DESTDIR is defined two times: the one I want, and the default one. How can that be?
Makefile header:
# Command: $(QMAKE) -spec /opt/zaurus/build/tmp/staging/i686-linux/share/qmake/linux-oe-g++ -after "TMAKE_CFLAGS-=-fgnu-linker" "TMAKE_CXXFLAGS-=-fgnu-linker"
"TMAKE_LFLAGS+=-L/opt/zaurus/build/tmp/staging/arm-linux/lib" "TMAKE_LFLAGS+=-Wl,-rpath-link,/opt/zaurus/build/tmp/staging/arm-linux/lib" "DESTDIR=/opt/zaurus/build/tmp/work/armv5te-linux/freenote-1.12.0-r0/FreeNote/output" "DEFINES+=QWS" "LIBS+=-lqpe" "CONFIG+=qt" "LIBS-=-lstdc++" "LIBS+=-lsupc++" "DESTDIR=/opt/zaurus/build/tmp/work/armv5te-linux/freenote-1.12.0-r0/FreeNote" -o Makefile FreeNote.pro