Add a Custom Form on Billing Record Object

We need the ability to attach a custom form to a billing record.

Use case: some of our projects have multiple billing records. On a single project, one billing record might be billed to department #12345. The 2nd billing record will be billed to department #67890. When sending the exported excel file to finance, we need the department number to be accurate. Currently we have to pull in that field from the project level, which can only have one value and we have to manually change it to the correct one after exporting.