The following AddOn package make do what you want.
It creates a second delayed stream that the players subscribe to. The addon has a simple module that is used to start & stop the delayed streams using a flash app.
The problem with trying to buffer the original source stream is that the players will normally try to connect and start at the live end of the buffer instead of the beginning. By using the delay package, the original source will be read as it comes in but will only be made available after the delay period has expired. It works on the stream timecodes so if the encoder is slow to send data (up to the delay time), it shouldn’t affect the playback.
The sort buffer probably wouldn’t work in your case as it buffers based on the system time that the packets arrive at the server. If they arrive late then they will be held in the sort buffer and will be sent out to the player late. This buffer is used in cases where the encoder sends video & audio packets that are out of order.