Combine 2 forms on the server-side

I have one form that a customer fills out with 30 fields.
Later, they fill out a second form with 100 fields.

How can I combine them (into one entry) so that we can do calculations on the values of these fields using GravityView gv_math? I know it doesn’t work with data from multiple forms (if there was a workaround, I wouldn’t be typing this). The final product uses some graphing to show their computed values.

Aside from the klunky solution of combining the forms with hidden fields and values on the browser, how would I be able to stitch the two entries together or update their previous entry on the server-side? I’d prefer to avoid exposing any of this stuff on a form that can just get inspected by a nosy-competitor.

Is there some sort of gform_entry_id_pre_save_lead or gform_pre_submission trick that I can use to write the data to a single