From the inside!
Consider inserting the pins from inside the cabin. This is a very clean approach and really isn't that hard to install/remove.
I installed the lower cowl, pushed the hinge pin up to the firewall and marked where it contacted. I drilled a hole just big enough for the pin to slide through. Put a small 90 degree bend on one end of the hinge pin so you can hold on to it. You can install a small block on the inside to secure the pin in place.
To remove, I just sit sideways in the seats and reach under the panel and slide them right out. To put them in, I first lean over the side of the plane and get the pin stuck in the hole and started on both sides, then I can climb in and push them the rest of the way. Sounds worse than it is.
You could improve the accessiblity by running some small ID tubing from the hole in the firewall to the subpanel and secure it. Then it might be easier to install/remove.
Just a thought.