The end result looks pretty neat I think.
So the first thing you will need are some wire grips. I used the 3mm galvanised type (from Bunnings). These fit perfectly onto the Detolf metal supports, even though those supports are 6mm in diameter.
I've positioned the wire grips about 19.5 cm above where the existing shelf supports are, that puts them pretty much in the middle on the available space between existing shelves. Of course this distance is up to you, you could even slant your shelves if you want!
I've faced the nut side of the wire grips parallel to each other looking into the cabinet. I've seen others place them on a 45 degree angle but I really didn't like that positioning.
The new shelves that I had cut are slightly larger than the original Ikea shelves that come with the unit. These are the dimensions of the new shelves:
381mm x 299mm x 3mm
At that size these shelves fit perfectly between the wire supports. I am not sure why Ikea's original shelves stop short of the wire supports, the bigger size gives more surface area and just looks better.
The glass then rests on top of the wire grips. I would also recommend putting some clear rubber grips on the glass shelves where they touch the wire grips. I couldn't find any at home so went without them, but it would prevent any scratching/sliding of the glass.
I've also written another article that may be interesting - Dust proofing the Ikea Detolf display cabinet to keep your collection pristine.
That's it, enjoy!