Hello Greg, Ben here - your Shopify Guru!
You can use liquid in your additional contents and scripts page. So just wrap your redirect script in some logic.
{% for line in line_items %}
{% if line.product.handle == "Product-handle-for-redirect" %}
REDIRECT SCRIPT HERE!!!!
{% endif %}
{% endfor %}
Just replace the Product-handle-for-redirect with the handle of the product you wish to redirect. This will work even if the product has variants too.
I hope this helps! Feel free to reach out if you have any further questions :)
Cheers,
Ben C - Shopify Guru
Support@Shopify.com