Prefill fields, on a custom form on a request queue, based on the user submitting it.

We would like to add user fields to a custom form that we use in request queues that will prefill based on the request's primary contact. For example, we would take populate fields for the user's phone number, email address and location based on who the primary contact is. There may be ways to make this to work after the request is submitted, using tokens, but we would like the fields that prefill to have the ability to be changed it if the information is incorrect.