However I believe a 4 day old larva is too old.
I use 1-2 day because after the second day the diet changes.
Also you can buy cell cups if you dont want to go through the trouble of making your own.
I just checked and have capped queen cells from this method. All "I" did was make one of my colonies queenless and broodless...selected a full frame of brood from another colony...identified larva of the correct age...cut the bottom of those particular cells down to the midrib...and placed that frame into the queenless colony. It worked. Those cells that I altered all had queen cells drawn from them.
Give it a try!