I think I found a workaround but not sure if it will work. At the airport I am picking up from, Alamo and National share the lot space. I was able to book a hybrid car on Alamo.com, and my full size car on National.com. My plan is to go out to the lot and tell them I am here for the hybrid, which would be put aside for me, and then drive it out of the exit as a National rental. I doubt they will have a problem with it. If it works, this would be my go-to strategy for making sure one of these cars is available for me.