libpq equivalent of jdbc:default:connection

I am rewriting a pljava procedure in C++ with libpq. This procedure needs to access some temp tables that the calling procedure creates and populates. It seems that the connection created by PQconnectdb creates a new connection (I have tried all permutations of conninfo I could think of). Since the connection is new, the temp tables are not available obviously. On the pljava side, we simply created a connection with DriverManager.getConnection("jdbc:default:connection"), which behaved admirably. Is there a way to accomplish similar behavior with libpq?

Best,

Jim