Simply keep repeating the reply message payload until the next message payload comes in from the ETs.

E.g. Earth receives the message: "How are you".

Then we send back in a nob-stop loop the message "We are fine. how's the weather?"

95 years later the aliens receive our message and immediately fires back their response "Great weather, here are some technologies that we think you may find useful"

However this message still needs another 95 years to travel to earth...

Thus we keep repeating our "We are fine, hows the weather?" message until 190 years later until their next message reaches us, at which point we can reply with

"Thank you for the tech, however it is about 200 years to late to be useful, nonetheless culturally interesting. Here's a Rick Roll in return."