asdf-config provides two new commands configure-op and initialize-op. configure-op keeps a registry of key-value pairs that initializes a variable after load-op completes. initialize-op depends on configure-op and will call a special package init function to, for instance, load data from a data directory after installation.
A single asdf-config source file can be downloaded from http://web.media.mit.edu/~eslick/asdf-ext/
At some point I'll make this asdf-installable