When you warm up before and even and then get teleported to the start area, one fit file is created for the warm up and one for the event and warm down.
I love to be able to simply ride into the start area and join the next event that way. When in the start area your workout would essentially be paused until the actual start of the event and also perhaps logging lap messages into the fit file so that it can be analysed if required.
Maybe evan have a small loop track that you could ride around and then ride into the start area just before the event starts.
This would then create just a single fit file and record all your warm up time too.