How can I append a string without | in this SQL injection?

The query looks like this:

INSERT INTO log VALUES ('abc: INJECTION')

I can inject like this:

INSERT INTO log VALUES ('abc: ' + 123 + ')

which results in the value 123 being inserted because the whole value gets cast to an integer.

I want to insert a string like this:

INSERT INTO log VALUES ('abc: ' || unhex('3120389123912') || '')

but the concatenation character | is filtered.

How can I insert the result of unhex() or similar to bypass the other character filters without using | to concat it?