Workaround : cache the computations,not the plotting itself (which
should be fast,and must be made on every table, anyway...) :

#+options: toc:nil author:nil

* Main text

Use of a static table:

#+call: timeit()
#+call: testplot[:file test0.pdf](data=table0)
#+call: timeit()

Use of a slow function:

#+call: timeit()
#+call: testplot[:file test1.pdf](data=table1)
#+call: timeit()

Use of a /cached/ slow function:

#+call: timeit()
#+call: testplot[:file test2.pdf](data=table2)
#+call: timeit()

* Annexes :noexport:

This is not exported, but computes results.

#+name: timeit
#+begin_src emacs-lisp
  (format-time-string "%Hh %Mm %Ss")
#+end_src

#+name: table0
| Val | Square |
|-----+--------|
|   0 |      0 |
|   1 |      1 |
|   2 |      4 |
|   3 |      9 |
|   4 |     16 |
#+TBLFM: $2=$1^2

#+name: table1
#+begin_src emacs-lisp
  (sleep-for 5)
  (setq s ( list (list "x" "x^2") 'hline))
  (dotimes (i 5 s) (setq s (append s (list (cons i (list (* i i)))))))
  s
#+end_src

#+RESULTS[46320b31c46cef901580bad78aee7032d97ffe64]: table1
| x | x^2 |
|---+-----|
| 0 |   0 |
| 1 |   1 |
| 2 |   4 |
| 3 |   9 |
| 4 |  16 |


#+name: table2
#+begin_src emacs-lisp :cache yes
  (sleep-for 5)
  (setq s ( list (list "x" "x^2") 'hline))
  (dotimes (i 5 s) (setq s (append s (list (cons i (list (* i i)))))))
  s
#+end_src

#+name: tf
| festfile.pdf ]

#+RESULTS[46320b31c46cef901580bad78aee7032d97ffe64]: table2
| x | x^2 |
|---+-----|
| 0 |   0 |
| 1 |   1 |
| 2 |   4 |
| 3 |   9 |
| 4 |  16 |

#+name: testplot
#+begin_src gnuplot :var data=table0 :exports results
  reset
  plot data with linespoints
#+end_src

HTH,

--
Emmanuel Charpentier