How can streaming replication be kept lagged by a certain 'delay' time?

Postgres has had [streaming replication](http://wiki.postgresql.org/wiki/Streaming_Replication) since 9.0 and since 9.1 it is possible to pause and resume the application of the streamed WAL records using [pg_xlog_replay_pause() and pg_xlog_replay_resume()](http://www.postgresql.org/docs/9.3/static/functions-admin.html#FUNCTIONS-RECOVERY-CONTROL) . As far as I can tell, there is no built-in way of keeping the application of WAL deliberately lagged by a specific time period (eg 24h). Have I missed a built-in way of achieving this and if not, how should I approach doing it some other way?