Set parameters values depending on other parameters

Is it possible in the Bex to have a parameter to be used to load data from another infoprovider (then the one of the actual query) in order to populate a select-option in the query ?

- a Customer exit variable seems to be able to only change its own values. It have no access to the other variable and parameters ?

- Replacement path seems to only be based on kind of "hard coded and unchangeable" selections.

So how to do that ?

I also think to use RRI by doing a 1st query but I wonder if all the result of the 1st query (lets say all the orders numbers) could be transfered into the orders select-option of a 2nd query ?