1. Create a new screen and drop this web block on that screen.
2. Assign launch url to full url of home page of your screen.
3. Assign invalidpermission screen full url to insufficiantPermissionURL property.
4. Optionally can pass button text in searchButtonLabel property.
Create a menu item and enclose in if block and set condition to check "CheckLoginAsOtherUserRightsRole(GetUserId())"
Assign "LoginAsOtherUserRights" to appropriate users only via service center. You are done.
Users list already has paging implenmented.
Will upload sample application shortly.