Thanks for the link @martindevans
So it looks like each client sends their full state to the server, which assumedly just forwards it naively to all other relevant clients. Makes sense since this server isn't a ksp instance and therefore doesn't have much insight into the spatial relationship between players.
That eliminates a lot of possible interpolation solutions, but it seems that a client side receive buffer could fit into their current code. I'll have to dig deeper to see if they frame stamp or timestamp packets, but at the expense of latency, jitter caused by changing network conditions could be drastically reduced.
Interestingly, due to the trusted client architecture, two buffers would actually be required. One on the server to smooth out received client state updates, and then one on the client to smooth out received server forwarding updates.