I've solved the first problem, using a something similar to what has been
suggested here:
http://stackoverflow.com/questions/10295177/is-there-an-equivalent-of-org-modes-b-ignoreheading-for-non-beamer-documents

The solution is to define
#+begin_src emacs-lisp
(defun sf-ignore-headline (contents backend info)
  "Ignore headlines with tags `ignoreheading" or `columns'."
  (when (and (org-export-derived-backend-p backend 'latex 'html 'ascii)
             (string-match "\\`.*\\(ignoreheading\\|columns\\).*\n"
                           (downcase contents)))
    (replace-match "" nil nil contents)))

(add-to-list 'org-export-filter-headline-functions 'sf-ignore-headline)
#+end_src emacs-lisp

This removes headlines with tags "columns" (or "ignoreheading", for that
matter), which is what I wanted. Any ideas for the second problem? I.e.,
how to get rid of the BMCOL in export to latex/html/etc. while keeping the
headlines/content?

On Wed, May 14, 2014 at 5:51 PM, Seb Frank <sebsfrank@gmail.com> wrote:

> Hi,
>
> I'm interested in using org-mode to generate beamer slides and an
> article-like printout (using the article class, usepackage{beamerarticle}
> and latex export) from the same source, and I am running into two problems
> with the export to article when there are multiple columns.
>
> 1.) I often use an empty headline with B_columns tag to allow me to
> specify top alignment. E.g.,
>
> #+begin_src org
> *                                                             :B_columns:
> :PROPERTIES:
> :BEAMER_env: columns
> :BEAMER_opt: T
> :END:
> ** Column 1                                                     :BMCOL:
> :PROPERTIES:
> :BEAMER_col: 0.35
> :END:
> ** Column 2                                                :BMCOL:
> :PROPERTIES:
> :BEAMER_COL: 0.6
> :END:
> #+end_src org
>
> In the printout, this yields an ugly empty section with a number if num:t.
> Is there a better way to pass [T] to the title-less columns environment, or
> (less preferably) a way to specify a title for the section without it
> appearing on the beamer slide?
>
> 2.) In the above example, the B_columns and BMCOL tags get exported to the
> latex file for the printout (with an error because the underscore is used
> outside of math mode). Can these be suppressed?
>
> Thanks,
>   Seb
>