From the SSRS side of things, I would do this. (I know little about sharepoint)
- Create a text report parameter (@user in this example) and set the default value to the Built-In Field "UserID". The userid will be something like "DOMAIN\user".
- Create a dataset (siteid in this example) using the @user parameter to pull the current report runners site id. I had to create a lookup table in SQL specifically for this.
- Create another report parameter of whatever type is needed for siteid (@site in this example), and set the default value to "Get values from Query". Select the siteid dataset field as the default.
- Create a dataset (names in this example) using the @siteid parameter in the where clause.
- Set both parameters to "hidden".
This should allow the report to auto-execute and retrieve only the name values that match the current users' siteid.