Unfortunately, this is not possible with the Arduino IDE. The reason is that when you create the firmware (
.spk) for a new core, it overwrites the build of the previous core. This means that there is one
.spk file for only one core at a time. Otherwise you could use the following command to upload multiple binaries for all cores at once:
$ ./flash_writer -s -d -n <main spk file name>.spk <sub1 spk file name>.spk ...