The asdf-dependency-grovel uses an extended *macroexpand-hook* to find out dependency information. This seems to work better than implementation-provided xref facilities (at least as long as there are no "uses at compile time" queries in xrefs (-:)
For the latest version, you can find a public git repository at: http://git.boinkor.net/gitweb/asdf-dependency-grovel.git
There is a more modern and featureful (and better-debugged) version of adg that's part of the xcvb project, at http://common-lisp.net/gitweb?p=projects/xcvb/asdf-dependency-grovel.git;a=summary;js=1
asdf ASDF-Extension