The easy way is to just use the LGCO curve and install it by dragging it into your curve folder and running the install command.
If you want to completely customize the amount of gloss yourself, simply open the blender tool. Copy the normal curve (with GCO) into the COOL column and the corresponding curve that is in the NGCO (no GCO) folder into the warm column. Alternatively you can copy the existing curve into the warm column and then just zero out the 256 numbers under LLK and that will do it too.
Then in the blender settings sheet, you will see ONLY the GCO change and nothing else.
This will allow you to change the amount of GCO across the entire tonal scale however you see fit.
ps: Related to x900 printers and GCO, I am working on a new driver that significantly improves both dot placement and dot size and dither and microweave on these printers and enables a higher amount of GCO.