I'm not familiar with particle systems and cache but as far as i know, the cache is saved to the particle system container object by default. So without using the external option, you could try to append (File>Append) the blender file, and chose the emitter object.

Hope this will work, I'm not able to test this solution right now.

I'm not familiar with particle systems and cache but as far as i know, the cache is saved to the particle system container object by default. So without using the external option, you could try to append (File>Append) the blender file, and chose the emitter object.