EXECUTE stmt USING expression
EXECUTE ... USING requires host variable names, not expressions, while SUBSTRING(whatever) is an expression. You will need to declare four host variables, assign results of the SUBSTRING(...) expressions to them, then use those variables in the EXECUTE statement.

Alternatively, you could move expressions to the dynamic statement itself:

set insert_into_info = 'INSERT INTO MYLIB.' || info || ' (
      CICUST, CIINF1, CIINF2, CIINF3, CIINF4, CISAD1, CISAD2,
      CISCTY, CISSTA, CISZIP, CISCRY
    ) VALUES (' || NEW_ID || ', substring(?, 1, 40), ' ||
    'substring(?, 41, 80)' || ... 
...
EXECUTE s1 using paddedComments, paddedComments, ...