[O] Sum marked values in table

[Stefan Nobis]

Hi.

Is there any way to somehow mark cells in an org-table and then sum
over all marked cells of the whole table. For example in the following
table I marked some time values bold:

  |        | Col 1 | Col 2  | Col 3  | Col4 |      Sum |
  |--------+-------+--------+--------+------+----------|
  | Row 1  |       | *1:00* |        |      | 01:00:00 |
  | Row 2  |  8:30 | 6:30   | *7:00* |      | 22:00:00 |
  |--------+-------+--------+--------+------+----------|
  | Sum    |       |        |        |      | 23:00:00 |
  | Marked |       |        |        |      | 08:00:00 |
  #+TBLFM: @>$>=??????::@>>$>=vsum(@<<..@>>>);T::$>=vsum($<<..$>>);T

Exist some clever trick to be used as formula for @>$> or is a custom
lisp function needed for this?

-- 
Until the next mail...,
Stefan.