Counting rows in a PL/PgSQL CURSOR without fetching?

Hi all.
Is there a way in PL/PgSQL to get the number of rows resulting from a:
    OPEN curs1 SCROLL FOR EXECUTE query;
before actually fetching any?

Unuckily
    MOVE LAST FROM curs1;
won't work with
    GET DIAGNOSTICS cnt = ROW_COUNT;

Any hint?