Fluent Forms Pro + Stripe — looking for a workaround without rebuilding the payment flow

Building a service booking site for a notary business in New York (WordPress + Elementor Pro + Fluent Forms Pro + Stripe). The forms have conditional pricing logic — deposit vs. full payment options with add-on fields that conditionally show/hide based on selections.

Client now wants to add tax collection to full-payment transactions only. The problem: Fluent Forms passes a fixed calculated amount directly to Stripe Elements.

What's the best way to calculate and display a tax amount to the user before they hit the Stripe payment step in Fluent Forms?