Unfortunately, you only have two choices - both will take some doing:
1) Manually change the datasource as you are doing now.
2) Use code (.NET or Java) to change the datasource. If you or some one in your org knows .NET or Java, this might be a trivial exercise. If you'd have to learn .NET or Java, stay with manual update 
- Ludek
Senior Support Engineer AGS Product Support, Global Support Center Canada
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