I'm trying to auto-fill unique record specific field inputs that I have in my Contacts and Deals modules onto Invoices created from the record's finance suite related list upon creation.  One example is a field called "Job Number" that I have in my Contact and Deals modules which is also a field on the invoice.  I want this to auto-fill on the Invoice creation screen based on the record's value (contact/deal job number) for the field of the same name on invoice.

When I was using the CRM Quotes/Invoices modules, I was able to map this with custom functions but it would only populate after the invoice or quote was created which is no bueno, we need it to auto-fill on the creation step since a PDF is automatically emailed with the invoice on creation and was missing.  I switched to the Finance Suite integration as we use Books extensively and it just made more sense for most of our processes but I can't even figure out a way to map it after creation much less auto-fill on the creation step with the Finance Suite integration.

Does anyone have any experience with this or know what language to use on a custom function to accomplish this?  Zoho has been great for a lot of my processes but simple field mapping is sorely lacking and requires too many workarounds for what should be a basic feature between modules.  Just having lead conversion mapping for leads to contacts only doesn't cut it.