Can Apache 2.4 run setuid root CGI binaries?

Note that I'm not asking about suEXEC, because the binary must be setuid root, and suEXEC doesn't allow root to execute CGI programs. I need to carry out a one-time configuration during system installation, via Apache. To do this, the client POSTs a request to a setuid root binary (compiled C++, owned by root:root, mode u+s). This almost works: the script does run as root, and modifies system files as required. However, it does *not* return stdout to Apache, so Apache thinks that it dies without producing any headers. Apache's error log contains nothing useful (just the usual 'no headers' message), and the CGI log/debug file also contains nothing useful (it just gives an empty %response, with nothing shown for %stdout or %stderr). I've tested the binary by running it on the server from a script which supplies the required POST data on stdin, and records stdout and stderr. It also runs it under valgrind. However, valgrind can't (easily) run setuid binaries, so I revert the binary to a plain 755 mode, and run the test script as root. In these conditions, the binary performs exactly as expected: valgrind reports no errors, stdout is a valid HTML response with status 200, and stderr contains only the valgrind output. Any insight appreciated.