A colleague pointed out to me that specifics of your question is not answered in the references I offered earlier. Let me try to rectify that.
Could you please check out APPLY_FILTER in the SAP HANA SQL Script reference. This might be what you are looking for. In this case you will not need to use "EXEC 'sql_string'. You can do the following instead:
temp_result = SELECT c1 c2.. from T1 ...; result = APPLY_FILTER(:temp_result, :my_dynamic_where_clause)
Don't be afraid that temp_result will be fetched and later filtered. If you do not read temp_result only result will be fetched after applying the filter.
Hope this answers your query better.