Error when rewriting a query into multiple queries

Dear Sir or Madam,

I'm trying to add progressive query into Postgres. Assume a query 'SELECT * 
FROM hugetable', my idea is to rewrite it into several queries as
    'SELECT * FROM hugetable TABLESAMPLE SYSTEM_TIME(500)'
    'SELECT * FROM hugetable TABLESAMPLE SYSTEM_TIME(1000)'
    'SELECT * FROM hugetable TABLESAMPLE SYSTEM_TIME(1500)'
the first query will provide real-time results to the user and the following 
queries will return later for more accurate results. However, I got a 
'[42601]: ERROR: cannot insert multiple commands into a prepared statement' 
error after I modified postgres.c or parser.c. Is there any way to do it on 
the server or it's better to do it in the application? Thank you for your 
help.

Best regards,
Wang