Well, in case you want to use only the pressure sensor at aspirin (having your own IMU), you want to disable the slaves on Aspirin 2.1 too. I currently have an option in rotorcraft makefile https://github.com/podhrmic/paparazzi/blob/master/conf/firmwares/rotorcraft.makefile#L140 
Maybe adding #ifdef into Aspirin driver would be the solution?