I just looked at the H&R website - They have a spring set specifically for the five. Drops it 1.4 in front and 1.3 in the rear - Their PN 29152 - It is a different PN than the Mazda3 so I assume that the spring rates are diffferent. For comparision, the AutoEx springs are an aprox 1.2 drop.
There is also the possibility of using an airbag strut system from Air Ride - This fellow did just that with his 2004 Premacy -
http://www.cardomain.com/ride/701041
I just think that finding room for the tank,pump and valves would be a problem.