This is based on the respectve patch from NixPkgs, but with the parts pinning
mysql and postgresql executables removed. The our package definition on why.

diff --git a/src/akonadicontrol/agentmanager.cpp b/src/akonadicontrol/agentmanager.cpp
--- a/src/akonadicontrol/agentmanager.cpp
+++ b/src/akonadicontrol/agentmanager.cpp
@@ -61,7 +61,7 @@ public:
                 []() {
                     QCoreApplication::instance()->exit(255);
                 });
-        start(QStringLiteral("akonadiserver"), args, RestartOnCrash);
+        start(QLatin1String(NIX_OUT "/bin/akonadiserver"), args, RestartOnCrash);
     }
 
     ~StorageProcessControl() override
@@ -84,7 +84,7 @@ public:
                 []() {
                     qCCritical(AKONADICONTROL_LOG) << "Failed to start AgentServer!";
                 });
-        start(QStringLiteral("akonadi_agent_server"), args, RestartOnCrash);
+        start(QLatin1String(NIX_OUT "/bin/akonadi_agent_server"), args, RestartOnCrash);
     }
 
     ~AgentServerProcessControl() override
diff --git a/src/akonadicontrol/agentprocessinstance.cpp b/src/akonadicontrol/agentprocessinstance.cpp
--- a/src/akonadicontrol/agentprocessinstance.cpp
+++ b/src/akonadicontrol/agentprocessinstance.cpp
@@ -62,7 +62,7 @@ bool AgentProcessInstance::start(const AgentType &agentInfo)
     } else {
         Q_ASSERT(agentInfo.launchMethod == AgentType::Launcher);
         const QStringList arguments = QStringList() << executable << identifier();
-        const QString agentLauncherExec = Akonadi::StandardDirs::findExecutable(QStringLiteral("akonadi_agent_launcher"));
+        const QString agentLauncherExec = QLatin1String(NIX_OUT "/bin/akonadi_agent_launcher");
         mController->start(agentLauncherExec, arguments);
     }
     return true;
diff --git a/src/server/storage/dbconfigmysql.cpp b/src/server/storage/dbconfigmysql.cpp
--- a/src/server/storage/dbconfigmysql.cpp
+++ b/src/server/storage/dbconfigmysql.cpp
@@ -209,7 +209,7 @@ bool DbConfigMysql::startInternalServer()
 #endif
 
     // generate config file
-    const QString globalConfig = StandardDirs::locateResourceFile("config", QStringLiteral("mysql-global.conf"));
+    const QString globalConfig = QLatin1String(NIX_OUT "/etc/xdg/akonadi/mysql-global.conf");
     const QString localConfig  = StandardDirs::locateResourceFile("config", QStringLiteral("mysql-local.conf"));
     const QString actualConfig = StandardDirs::saveDir("data") + QLatin1String("/mysql.conf");
     if (globalConfig.isEmpty()) {
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