What is a practical, manual (pen & paper) method to generate a cryptographically-secure key for a one-time pad using natural text as a seed?

I thought I had found an answer to my question when I read this:

link

There, one of the posters effectively claims that your seed word's gematria mod 10 is a random number. In other words, sum the letters of a word, treating each letter as the number of its place in the alphabet. Then divide it by 10 and the remainder is your random number.

Another poster even "proves" this digit is random by showing a graph representing a flat distribution of digits after inputting thousands of common English words as seeds.

But when I tried this, I got a very UNFLAT distribution. 9 and 1 are TWICE as common as any other number except 3.

So, is there a practical way to manually (with pen and paper) generate a cryptographically-secure pseudo-random number using natural text as a seed?