The latin-1-postfix method allows for inserting a lot of nonletters.

I am not sure what you mean by "a lot".  Most Latin-1 non-letters do
not seem to be included.

I started writing changes to add ways to enter some additional
characters, shown below.  But I have doubts about whether these
sequences are good ones.  They might be inconvenient.

+  ("\"\"" ?¨)
+  ("''" ?´)
+  (",," ?¸)
+  ("* " ? )  ; Non-breaking space
+  ("+_" ?±)
+  ("-*" ?­)
+  (".*" ?·)
+  ("^*" ?¯)
+  ("c*" ?©)
+  ("l*" ?£)
+  ("p*" ?¶)
+  ("r*" ?®)
+  ("s*" ?§)
+  ("x*" ?×)
+  ("X*" ?¤)
+  ("y*" ?¥)
+  ("|*" ?¦)
+  ("1*" ?¹)
+  ("2*" ?²)
+  ("3*" ?³)
+  ("2_" ?½)
+  ("4_" ?¼)
+  ("3_" ?¾)
+  ("//" ?÷)