it is easily possible by humans
well not easy when you have multiple people in different time zones but not hard either

first everyone resets their computer to the same time zone
this is just so there no confusion about the time you're talking about

then the guy furthest away sends his wave and reports the time to impact
or the guy who sending the slowest wave
the wave that takes the longest to arrive is sent first

then everyone else sends to land at that same time

easy when there's little lag, harder when the server is a bit slow