I do all my guns by hand as well, but I put the end against the floor and use my body weight on the breech end, or if the barrel is installed I simply put it at 90 degrees. Piece of cake
I too use something smaller in the pin hole for guns that are harder to compress, like nitros, so it will align. I also often chamfer the internal part so the pin guides in better, and sand both the pin and internal hole if it's not a good fit. A Crosman nitro is a good example for that with it's one big pin going thru a steel block inside.
Some guns like Ruger or maybe it was Hatsan, or both, the internal block is plastic and an extremely tight fit. A little sanding and lube does the trick.
Here are some home made jobs:
http://www.airgunone.com/forums/showthread.php?t=5836 including plans I drew for someone which is the stick photoshop drawing under my screen name. If anyone has tried it they haven't told me, but I'm curious to hear. I think it's ideal for it's simplicity, low cost, and I believe it would be 10X or more faster than the normal ones.
So, any comments on the performance after the kit? I've been considering the vortek spring for my 350, just the spring tho. Seems the 350 and Ruger mag are underpowered for their size so I've heard really benefit. I do like the easy cocking of mine, 32lbs with the oem spring, but would trade for 40lbs if the power went up to say 28ftlbs. So if you have details like that I'd like to hear, but your overall opinion too.