Adding non template documents to existing custom workflows

We have a multi-signer\reviewer workflow that we use with templates we have created from standard home-buying contacts.  The salespeople execute the workflow and fill out the appropriate contracts for the homes we are selling. The contracts are standard and using them as templates is perfect.  What is not standard is we have several documents that we export from our home building software that are unique so it would not be effective to use a template, nor is helpful to copy and paste the information over to an existing template. 

We want all the signers and reviewers that are part of the existing workflow to review and sign these documents as well, but not sure of how we can include them without being a template during workflow execution.  It would be acceptable if they were not part of the original workflow with the contracts, we ultimately want to avoid the salesperson having to add all the people to sign manually which is error-prone.

Thank you in advance!