Could looping the pre-heat hoses to the exhaust cause harm?

My cat was stolen, and my replacement options are limited. I found a Magna Flow replacement that doesn't include any sort of preheat connections. So the engine coolant hoses that run to the exhaust would just need to be connected together. Is this potentially harmful to the engine? It seems like it would just make the engine take longer to heat up and thus the engine would run longer after a cold start, and thus reduce gas mileage. Are there any other concerns?

 

Forgot to mention it, but here is the link to the magnaflow part:
https://www.magnaflow.com/products/52453-magnaflow-2010-2015-toyota-prius-oem-grade-federal-epa-compliant-direct-fit-catalytic-converter