Post FI Document without CO Object when

We have an issue where a document posted to a GL account without a cost center (cost center should have been required) because the cost element for the account had not yet been created. That cost element has subsequently been created. We would like to post an entry to reverse the original document (leaving the cost center blank), but the G/L account now requires a co object so we are stuck in a spot where we cannot reverse our original error.

To clarify here are the steps that we took:

Create a G/l account.

Post a document without cost center.

Create a cost element for the GL account

Attempt to post a document with out a cost center ... no longer possible becuase CO object is required for the account.