Custom script for Clickfunnels

Hey guys! Long time lurker, first-time poster. I've got a quick question about a custom script in Clickfunnels. If I want to create a script where a piece of information that a visitor entered in a text field would be incorporated in to their URL once they click a button, how would I do that?
For example, I'm selling courses on Thinkific, and I've got my clickfunnel connected directly to Thinkific's checkout page because Thinkific's landing pages suck. The only issue is if they want to enter a coupon code, they can't because I'm bypassing that part of Thinkific's checkout process. Thinkific has the ability to apply a coupon code that's embedded in the URL. Is there a way I could create a text field on a Clickfunnnels page where they can enter their coupon code, then when the click the link to checkout, the code they entered will be encorporated in to the URL so it's picked up by Thinkific?
Example: my normal checkout page would be accessed at: https://courses.worshipsoundguy.com/enroll/149732 but if you add ?Coupon=[COUPONCODE] at the end, it'll go to the checkout page with the coupon already applied. Is there a script that would take the coupon code they enter on the page and insert it in to the URL in place of [COUPONCODE] when they click a button?
Thanks!
-Johnny