He had been trying for a long time to find a solution but was unsuccessful. However, Luke came up with a solution that would allow for the deployment of SW without a disruptive flag day using a new P2SH-like scriptPubkey type. This approach requires the scriptsig for the scriptPubkey to be empty during the soft-fork.The signatures are not covered under txid but are carried alongside and then committed to in blocks in a separate hashtree. The only disadvantage to this approach is that it disrupts the normal relay handling process, as relay transporting extradata needs to use a different hash that includes the witness or have a separate mechanism for witness transport.