PostgreSQL (or rather, DBD::Pg) allows dollar notation too, so you can re-use those. (Must start at $1, but can be used in any order in the query), see DBD::Pg docs, under 'placeholders'.

I normally set $dbh->{pg_placeholder_dollaronly} property so I don't start using the questionable question mark.

(Of course, if your SQL is submitted to other DBMS than (just) postgres, you'll have to think of something else)

edit: Oh, I see you're also the last_insert_id guy. That means you're mucking around with a lesser db than PostgreSQL and that the above should be ignored till you upgrade to the better system