ODBC API SQLFetch() Asynchronously
I don't think async execution will accomplish what you want. SQL Server returns results to the client as they become available if you've specified a fast-forward ODBC cursor type. 

Separately, displaying partial results in a GUI interface while the query is still running may require special programming techniques. That's not really a database problem so StackOverflow would be a better forum if you have additional questions about that.