Creating temp tables inside read only transactions

I have a function that creates a temp table, populate it with results
during intermediate processing, and reads from it at the end. When the
transaction is marked as read only, it does not allow creation of temp
table, even though there are no permanent writes to the db. Are there
any workarounds? The following block errors out.

SET TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
create temp table test(test int);