"The addition of components to a PC, such as adding a second hard drive which did not exist during the original activation, would not trigger the need for a reactivation." - from click here
So when you install XP to the fixed master, disconnect the slave drive. Subsequent addition of the different slave drives will not trigger reactivation.
Even if you have a slave drive connected at the time of installation or activation of XP, changing the slave drive (no matter how many times) will still only count as one change, which will not trigger reactivation.