I am not sure whether the parameter is changeable. However, it is important to say the OLAP connector is not good for large sets of data (but rather to use the advantages of the Business Logic implemented in BEx queries).
I can suggest to options
1. If the data is stored in a DSO - try to extract the data from the Active table using the SQL connector
2. If you have to use the OLAP connector to extract query results, try to use loops and extract a slice of the data using a query variable.