myDSL Extensions (deprecated) :: Help, how do I add myDSL extensions offline

I don't mean to hijack...I assume this is a related topic....
Something I've been thinking about a lot is how that backup partition is used. Does DSL use the device file to obtain myDSL files? I've been wondering if it's possible to specify a subdirectory instead of just a partition, but I assume if it uses the device file directly then this wouldn't be possible. Is that correct?

original here.