"Set Content Approval Status" activity raise "Access Denied" error since creator has no "Design" permission

In my workflow for a InfoPath Form Library designed by SharePoint Designer 2007, I set the creator of form has only "Contribute" permission which could not approve the form; and I use a "Set Content Approval Status" activity to approve the InfoPath form.

But when execute the "Set Content Approval Status" activity to set the InfoPath form to "Approved", I found that an error "Error updating a list item" was found in workflow history, below is the detail of the error history:
    Date Occurred: 8/1/2009 22:27
    Event Type: Error
    User ID: System Account
    Description: Error updating a list item
    Outcome: Access Denied

I investigated this problem, and found this is caused that the workflow is started by the creator of the InfoPath Form, but when update the "Approval Status", it need Design permission, since the creator has no enough permission, it failed to update this InfoPath form with "Access Denied" error.

How can I resolve this problem? I could not give the creator "Design" permission since this is conflicted with the bussiness requirement. Is there any way to update the "Approval Status" without design permission in workflow?

Thanks!