Getting a document re-signed by one signatory

One of my signatories signed without a witness present, so I need the signatory to re-sign (in front of a witness) who then also signs my document (to confirm witnessing the signatory sign).  The signatory is the last of several other signers, so I don't want to have to get everyone to sign the document again if I can avoid it.  Is there a way I can re-send the document as signed by all other parties so that the last signatory can re-sign?

Another option is to break the document into two counterparts - one as signed by all the other parties and one as signed by the last signatory and witness.  Can I finalise the first counterpart (as signed by all the other parties) and remove the final signatory's signature?

Thanks