Why would it have to be "extra"? ISTM they could just train as they do now, except that they would concentrate all the ICE issues in the five hours in which they're flying with ICE.
Every new airplane type takes some type-specific instruction. True, it could count towards the FAA-minimum 40 hours, but almost no one takes a checkride with 40.0 hours in their logbook. I was a pretty dedicated student and at least a fair stick, and I was still in the 55-57 hour range when I took the checkride. Most people training at towered fields are in the 60-75 hour range at the ride.
Fuel isn't the dominant cost in flight training. (Source: I bought my first airplane during flight training and have been flying for almost 2 decades now. Fuel is more than a rounding error, but tends to run around 1/4 of my all-in costs.)
Fuel isn't the dominant cost in flight training. (Source: I bought my first airplane during flight training and have been flying for almost 2 decades now. Fuel is more than a rounding error, but tends to run around 1/4 of my all-in costs.)