[Cooker] How to properly override C(++) lags for Makefiles generated by qmake?

I'm trying to build aqemu. It fails on printf format error, but
disabling it in specs is ineffective; Makefile is generated by qmake and
C(XX)FLAGS are statically set in Makefile.

Unfortunately using make CFLAGS=... does not work either because CFLAGS
are built from other variables as well:

CXXFLAGS      = -pipe -O2 -g -pipe -Wformat -Werror=format-security -
Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-
buffer-size=4 -Wall -W -D_REENTRANT $(DEFINES)

I hope, that it is possible to override template CFLAGS during qmake
invocation. Is it possible?