I made a chute out of a piece of aluminum I had. Bent 90 degrees and tapered on the end that goes into the wsm. Then I take a fireplace shovel, push the coals in the wsm to the rear and add the new lump on the front side by pouring down the chute.
Do not do this if you have unfoiled meat in the cooker as you will have dust. You really shiould do what they call the hot squat. That involves taking the lid and center section off and adding right on the coals in the ring. You need welding gloves as the cooker is hot and mounting Genie garage door handles on the middle section helps to do this.
Smooth Smoke BBQ Team, KCBS CBJ, 2-WSM, Cajun Bandit Conversion, wsm 2880, Smokey Joe Mini wsm, Old Country offset, several kettles.