This can be done by starting the packet with the reference block height if multiple txins or multiple transactions are being sent in a single packet. If the application typically sends just a single transaction, a reference height that is a function of the current time can be used.There is a mention of the sender and receiver potentially not agreeing on the exact time, so different reference heights can be tried via brute-forcing until the transaction signatures validate. The email also includes a link to Peter Todd's website, https://petertodd.org, which may provide further information on this topic.