Ed wrote: "By my 10 minutes of research there is no easy way to do it and the hard way is gonna be really hard. "
I agree. Probably the hardest part for our cars would be retrofitting the sensor ring to the hubs on all four wheels. Really hard on the front, even more hard on the rear for a swing-arm and pretty easy out back for an IRS car. Then, you need to find an ABS system with integrated computer that works on a rear-wheel-drive car, like, say, a 2003 Mazda Miata, which happens to have an ABS system with minimal integration to the other on-board systems. BUT! The sensor biasing will be all off because the ABS system expects the weight in the front to be much greater (4X?) than our cars or the braking force up front will be too much.
And on, and on...... As Ed says - Really hard (unless you drive an SAS, which retained all that from the donor Imprezza).