Hi Parag,
1. As Raju said create a property in account dimension and fill that " Y " for the required accounts which are need to display in report. Do the same for the Product dimension also. while creating the report use dynamic filter by using the property it will fetch the accounts products which are enabled in the Property as "Y".
(For example later when they want different set of accounts just enable those accounts as "Y" under property column.)
2. If you want organization dimension only in the context go to options --> Context lock options -->hide and lock the dimension which are not required to display in the context.
Hope this will help,
Saida Reddy G