The around methed will look something like this
(defmethod input-files :around ((o asdf/bundle::gather-operation) (c system)) (unless (eq (asdf/bundle::bundle-type o) :no-output-file) (append (call-next-method) (remove-if-not (asdf/bundle::pathname-type-equal-function (asdf/bundle::bundle-pathname-type (asdf/bundle::gather-type o))) (mappend (lambda (c) (output-files 'process-op c)) (asdf/component:sub-components c :type 'wrapper-file))))))
To my taste it knows too much about ASDF guts, but maybe it is not too bad.