Hello Serdar,
There is no such option available to completely dynamically decide the possible back end for an OData call. The multi origin option is the closest possible feature to meet your requirement.
If you have configured all POSSIBLE the system aliases, then you can navigate to the desired destination at runtime using the following notation ;o=<ALIAS NAME>
Example:
/sap/opu/odata/IWFND/RMTSAMPLEFLIGHT;o=ALIAS NAME/CarrierCollection
Regards
Atanu