Create a file similar to the following:
personal_ws-1.1 en 2 wlkju yytuvze
Replace "en" with the language you're using and "2" with the number of words in the list. I've shown two nonsense words, but your list should consist of one word per line in a similar manner.
Save the file with a name such as .aspell.en.pws
.
This is an example command using a personal word list such as the one above:
$ echo 'foo yytuvze bar baz banana wlkju' | aspell -a --personal=./.aspell.en.pws --dont-suggest @(#) International Ispell Version 3.1.20 (but really Aspell 0.60.6) * * * # baz 16 * *