I was talking to Mike at Mazdaspeed today, and he mentioned that they have a new product: a rear hub with long studs already pressed in.
I won't post prices, but the delta between the stock part and the part with long studs is basically the price of the studs (labor's free!):
0000-04-5HUB-RR
@ HUB, REAR (W/LONG STUD)
Notes:W/ 2.75" LENGTH STUDS