on_sent_ok multiple redirects from dropdown

I have multiple contact forms using as class signups. Each form sends to different email address/different teacher, with different thank you page. I believe your situation is similar to mine. This is how I am doing it for now.

1) install PHP in post/page plugin (your choice)
2) create post/page for selecting 8 stores as dropdown
3) on select store, echo the appropriate contact short code
4) in Additional Settings in each contact form, you can insert on_sent_ok: location = thank you page/?var=store1msg etc.
5) create post/page where it will $_GET[‘var’] and echo appropriate message (optional)

Good luck ??