How to record additional details on terminate employment

Summary:

We want to capture additional information when a person ends an assignment or terminates their employment with us.

What have other people used to capture additional information on end assignments

Content (required):

We are looking to roll out manager self service using the V3 termination form. However we need to record additional details such as leave to be paid, where they are going to, etc. we had hoped to collect this information in a document of record but this relies on the manager remembering to add the relevant document of record in the flow. We need to capture this information at an assignment level rather than person level, so we know that additional flexfields at work relationship is not an option.