QProcess proc;
    QProcessEnvironment systemEnvironment;
    systemEnvironment.insert("PATH",systemEnvironment.value("PATH")+":/home/sasha/source/test/aaa");
    proc.setEnvironment(QStringList() << "PATH=/home/sasha/source/test/aaa");
    proc.setProcessEnvironment(systemEnvironment);

    proc.start("myprog --version");
    qDebug() << proc.waitForFinished();
    qDebug() << proc.errorString();
    qDebug() << proc.readAllStandardError();
    qDebug() << proc.readAllStandardOutput();

false
"execve: No such file or directory"
""
""

proc.start("/home/sasha/source/test/aaa/myprog --version");