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Accomplishing this was actually very easy and straightforward. Not sure if anyone has done it, but I haven't seen it mentioned so I figured I'd post it up.
After slimming the gate spring and deburring and polishing everything, I modified the gate so that I would no longer need a third hand for loading the magazine, and would no longer be launching live ammo at people behind me during the process.
I loaded one round and pushed it in until it was flush with the gate opening, and then marked the location where it rested on the gate with a sharp knife. I then used a dremel cutoff disk that was roughly the diameter of a shell base to carefully cut a shallow relief at the end of the gate for the shell to set in. The cut is made perpendicular to the gate, and parallel to the front face of the port. It needs to have a sharp edge, and cut so that when the gate is open, the cut angles inward slightly which helps hold the case in place.
Sorry about the following cell phone pics, but you'll get the idea. (I'll do some detailing on the gate notch before rebluing it).
I can now easily load the magazine with one hand by pushing each round in until it is flush with the front of the gate, at which point the gate catches the bottom of the case and holds it in place. As long as you don't push down on the cover with the next round and release the previous one, it is cake. On the last round, I just use my pinky to push it past the gate.
