(the exact names aren't important, it's only internal to GC)
Start Minecraft and then quit. CC/GC will create configs for three biomes with those names, which you can set to the appropriate IDs and whatever incidences/climates/etc you want. This will make them show up as full-sized biomes.
Oasis should appear as a sub-biome in Desert already. Gravel Beach isn't used. Gravel Beach as a full biome would be awful though. If you want Gravel Beach to show up as a beach for BoP biomes that would require some significant recoding inside GC (the beach code is inherited from vanilla and is a special-case mess).
Thank you for the fast answer. I've been playing with the configs for the last hours. I'm addicted.
Actually, what I'm trying to do is remove the Oasis sub-biome. I add it to the external biomes list, and generated the configs. On those configs, I set incidence to 0. But that didn't stop the Oasis from beeing generated as a sub-biome inside Desert biome.
Is there currently any way to stop specific sub-biomes from generating?