There is definetly still a lot of space for additional cooling without sacrificing too much space for the battery. A wider cooling thin stack with maybe a third heatpipe that goes to the should be an option. Pair that with a better thermal paste and the laptop should be able to handle a 45W TDP cpu. The ssd could also be moved to the side with the additional space.
Power consumption of the 45W cpus should also be very similar to the 25W options under light workloads and in idle
