Restricting Variable values in BEX query

Hi Friends,

I want to display the sales data in my BI report for 10 cities across world. User can select single or multiple cities at prompt level to see the data.

For this i have created cheracteristic variable of manual input type.

the problem is when user wants to select city values at variable prompt, F4 help showing all the cities available in my infoprovider. But i want to give him option to select only values from particular 10 cities. how to acieve this. please give your valuable solution.

Thanks

Vijay