How can I use the GCC -frandom-seed=<file name> option with the waf build system?

According to the GCC documentation the -frandom-seed=string should have a unique string for each compiled file, see GCC Developer Options. One common approach is to use the source file path. How can I teach the waf build system to use the source file path for the option? I tried to use -frandom-seed=${SRC[0].abspath()} in bld.objects(cflags=...).