Restrict Initiator from approving custom approval workflow

 hi,

i have created a custom approval workflow using sharepoint designer.
i used "collect data from user" and selected a approver to approve or reject a request.
when a request is approved i am updating the status of list item to "Completed"
when the approver tries to update a list item i was getting error so i have given "approve items " permission to the Initiator which i found in a article at
http://office.microsoft.com/en-us/sharepointdesigner/HA102098081033.aspx#5

now the workflow is working as expected but the problem is after giving "approve items" permission to the Initiator , the Initiator himself is able to approve the workflow.
which is not what i want.

"initiator should not be able to approve any workflow ."
only the approver should be able to approve workflow.

can anyone please give me a solution .
i need help ASAP.

any help is appriciated.

regards,
swastik.