Thanks for the additional info. If I understand correctly, you essentially want to provide those who pay via bank draft a reference number such that when you are informed of the receipt of a payment by your bank, you can do a find on the number and pull up the pending pay later contribution more easily than you would just by relying on a name - if that's the case, I would suggest you add a token to the for contribution ID and/or contact ID in the "Contributions - Receipt (on-line)" System Workflow Message Template provides content and formatting for the receipt. You can modify it from Administer > Communications > Message Templates > System Workflow Message and it is part of the email that they receive after registering and ask that they include that as a memo or a note when requesting the bank transfer. You will need knowledge of HTML to do this (which I do not have).
The link to the participant record will be preserved if you edit the pending pay later contribution to a status of "Completed" and include whatever other details of the payment that are pertinent (e.g. transaction numer, date, etc.).
Hope this helps,