ASDF and Allegro libs

Is there a standard convention for defining ASDF systems that require Allegro
 libraries, like Allegrocache, since you can't

   (asdf:operate 'asdf:load-op :acache)?

defining a component that contains

   (eval-when (:compile-toplevel :load-toplevel :execute)
      (require :acache))

seems like a bit of a hack...

thanks for your time

Nick