YOu have to add manually the queries everytime or else you have to store database details in some Excel file and using this loop through each row and load the data dynamically, everytime when a new database add it in the excel and for loop will load automatically.
-I do this successfully storing the database details in a xls and using a loop, as Jagan suggested.
It works great on 30+ databases, all of which are 10+ Gbytes and some 100+ Gbytes.
For each database I store a seperate qvd file which makes the incremental loads much easier than they would be otherwise.
Then in the qvw dashboard I do optimized loads of them via a loop using the same xls and concatenate them all together.
QlikView works really well with such concatenated Fact Tables and with QlikView's inherent data field de-duplication will most likely be the most efficient solution - dependent on the actual data values, occurences & spread.