Query plan optimization: sorting vs. partitioning

Hello list,

I have a large time-indexed table (states) partitioned into several
tables based on the date. The smaller tables are clustered by their
time indices.The main table is empty.

I need to select some data in the time order. When I query a separate
smaller table, the index is used an no sorting is needed. However,
when I query the main table, it occurs:
...
  ->  Sort ...
         Sort Key: ...
         Sort Method: ...
         ->  Result ...
               ->  Append ...
                     ->  Seq Scan on states
                           Filter: ...
                     ->  Seq Scan on states_20101206
                           Filter: ...
...

I see the database doesn't understand that there are no entries in the
main table, so it has to assume the Append data is not ordered. Is
there a way to avoid sorting?

Please CC me as I'm not on the list. Thanks in advance,

--
DoubleF