Have not tried that, but from all I have read it is not possible. There supposedly is a special added cable from the HP PCIe SSD card to the Z620 motherboard, and a BIOS update to let that work. The Z600 has no such motherboard header that can be enabled/modified by a BIOS update to enable the HP card.
However, there is a nice post for the Z600 where Brian describes getting a non-HP PCIe SSD card to work quite nicely, and hopefully he will update us on how things have gone since then. It is HERE.