There will be to much space betwen Chip and cooler without the pad.
Just set down the Memoryclock to the lowest possible and dont mind, the pcb can take a lot of heat.
Later you can install the Thermalpads if you got it.
To much space? The arctic silver ceramique would permanently stick the heatsink on.
It's a sort of adhesive, but permanent, it's basically a permanent adhesive form of Arctic silver 5, but made with ceramique.
It's a thermal paste, so it should do the same thing as the pads, there wouldn't be any space between.
Just don't have much experience with arctic silver ceramique, so am not sure if it's same to use on memory.
It was recommended by a friend to do this, I just don't know if he has much experience with GPU's in particular.