Yeah I think they took a big step backwards with the GX460 with those low profile rails... they look nice with nothing attached, but so much less functional compared to the raised rails of its predecessor the 470. they kinda improved it with the Blackline edition, went back to a raised rail, but they omitted the slot on the inside, so you still can't bolt anything to them. thankfully, they can all still be removed from the top, which opens up the options considerably.
our quick/easy solution for adding t-slot extrusions are called accessory angle brackets. but they don't work on GX460's, for the reasons just mentioned.