How can I redirect some traffic to new product pages on a single domain?

[domgreen]

Hi all I am very stuck on an issue and was hoping some one here may be able to help.

We are currently about to  roll out our headless Shopify store application. 
We have the requirement to use our new product pages while keeping the checkout and other shopify areas available on the store domain. 
We are a high traffic site on the shopify plus plan.

My initial thought was to put a reverse proxy over the store DNS then proxy requests to shopify or the new app. But through a fair amount of research it sounds like this would fail due to shopifys api rate limiting. 

Another option I thought was to redirect product pages during the rollout to the new site. This is not ideal as a user would move around subdomain and it also seems that you cannot redirect live pages in shopify. 

Is there any option that is possible to serve two applications on a single domain with shopify.

Thanks