There are a number of tricks for easing a fuel tank into a cramped location.

Rubberband the lines together at the loose ends and use a "fish" line. Nyrod works good to stick through the firewall and plug into one of the fuel lines. You then pull them through together. Other stuff works as a fish line etc etc

But your idea about the tank at the CG sounds good also. Putting it at the CG is going to make the extra small tank that's been mentioned a great idea. Or using a pump is a good idea. And muffler pressure may work to support that two-tank setup, but maybe won't.

You've not mentioned the model.