SharePoint List Permissions

What is the best practice for granting temporary permissions to a user to add/update a list item on a SharePoint list.  Barring a better solution it seems that I would need to

1. have a SharePoint security group with the desired permissions in existance
2. create a step after the task that will lead to an addition/update to the item that adds the task respondant to that security group
3. Perform the add/edit
4. create a step that removes the task respondant from the security group.

If there is a better/easier way to do this please let me know.