Do you need to buffer the data from the E220 ?
Why not just have the transmitter keep sending the data until it receives a acknowledge reply from the receiver ?
So the first send wakes up the receiver, which then waits for another packet and when it receives it sends an ack to the transmitter.
And if you switched to SPI based LoRa modules what you are trying to do would be a lot easier since the LoRa device of the receiver will keep the packet data until you read it out.