qmake custom compiler use output

[Skycoder]

I am using a custom compiler for qmake to create translations:

lrelease_compiler.name = lrelease ${QMAKE_FILE_IN}
lrelease_compiler.input = TRANSLATIONS
lrelease_compiler.variable_out = TRANSLATIONS_QM
lrelease_compiler.commands = lrelease ${QMAKE_FILE_IN} -qm ${QMAKE_FILE_OUT}
lrelease_compiler.output = $$OUT_PWD/${QMAKE_FILE_BASE}.qm
lrelease_compiler.CONFIG += no_link target_predeps

QMAKE_EXTRA_COMPILERS += lrelease_compiler

The compiler itself works as expected, but the TRANSLATIONS_QM variable stays empty. I want to use the out variable for a install target, as it should theoretically contain the qm-versions of the files, but it doesn't

message($$TRANSLATIONS_QM)
ts_install.path = $$[QT_INSTALL_TRANSLATIONS]
ts_install.CONFIG += no_check_exist
ts_install.files += $$TRANSLATIONS_QM
INSTALLS += ts_install

The message directive returns nothing, and the install target is not added to the makefile, i.e. running make install will not copy the generated qm files.

Is there a way to make use of the variable_out for that purpose?