How to phrase authors' contributions when the convention is that all team members are authors? The question
When a journal (such as one of the Nature family) asks for information about authors' contributions, what is the most effective way to answer this, to ensure that the co-authorship is assigned as intended, and to ensure that reality is represented: that the work is a product of the intellectual environment of the whole team; and that all members have contributed in various degrees to the analytical methods used, to the research concept, and to the experiment design. Is what I've just written there sufficient, or is there a more judicious phrasing that is accepted by heavyweight journal publishers such as the Nature Group?
The context
The primary context is publications from a team that works on the principle that all members of the team are to be named authors on all papers coming out of the team.
I'm very specifically looking for answers from editors who handle such papers; or from members of teams with similar rules. Answers from others are of course possible, but I'd value direct personal experience.
Here's the Vancouver Group's (International Committee of Medical Journal Editors) statement on the subject:

Authorship credit should be based on 1) substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; and 3) final approval of the version to be published. Authors should meet conditions 1, 2, and 3.
When a large, multicenter group has conducted the work, the group should identify the individuals who accept direct responsibility for the manuscript. These individuals should fully meet the criteria for authorship/contributorship defined above, and editors will ask these individuals to complete journal-specific author and conflict-of-interest disclosure forms. When submitting a manuscript authored by a group, the corresponding author should clearly indicate the preferred citation and identify all individual authors as well as the group name. Journals generally list other members of the group in the Acknowledgments. The NLM indexes the group name and the names of individuals the group has identified as being directly responsible for the manuscript; it also lists the names of collaborators if they are listed in Acknowledgments.
Acquisition of funding, collection of data, or general supervision of the research group alone does not constitute authorship.
All persons designated as authors should qualify for authorship, and all those who qualify should be listed.
Each author should have participated sufficiently in the work to take public responsibility for appropriate portions of the content.

The caveats:
 1. My field is not medicine: I've used the Vancouver Group's guidelines, as I haven't yet found any in my field.
 2. note that this is emphatically not about the ethics, pros and cons of such a rule. If you want to discuss that, please do so in chat. I may join you there as time allows
Related literature:

Author contributions audit, by Maxine Clarke on the Nature Nautilus authors' blog, lists example contributors' satements
Drummond Rennie discusses &quot;Authorship Credits&quot;
Academia and Clinic, by Yank &amp; Rennie: Disclosure of Researcher Contributions: A Study of Original Research Articles in The Lancet
and lots more at the US Council of Science Editors
If there is a requirement to list the contribution of each author, it seems the ethical way to handle it is, well, to list the contribution of each author.  If some authors did not contribute directly to the paper, you should state that.

It is unethical to try to conceal that some authors did not make a direct contribution.  Please note: Your team policy is what it is, and I'm not trying to judge the ethics of your team's policy.  I'm just saying that, whatever your team's policy is,  you must disclose it forthrightly, without evasion.  That's exactly the point of disclosure requirements!

(If you're not comfortable stating your team's policy explicitly, that might be a hint that it's time to consider changing the policy -- but until then, you must disclose it frankly and honestly.)