Something i found today is that you can change the dependency of parameters of your dataset by changing the order the the parameters in the data query. For example:
Selecting the internet sales amount with parameters promotion at the year 2008. This will give you all the promotions available.
Changing the order of the parameters
will get you all the promotions in 2005 as parameter values. This is very cool and I don’t know why i missed this all this time, read more at msdn