To keep it stored with empty chamber, full mag: Load mag. Depress shell release (next to trigger guard) to release a shell to the carrier (lifter). Put next to bed. When you need it all you have to do is pull/release the bolt handle.
To load the mag without getting Benelli thumb: Push the shell in with a quick shove, but.. and this is the key, Keep the knuckle of your thumb bent. Push the tip of your thumb straight in. Push with the tip of you thumb, not the pad. Your knuckle will keep the lifter up.
Don't try to ease the shell in. SHOVE it in hard, with the TIP of your thumb. A lot of people get their thumb caught because when they push the round in their thumb is up (the FONZ), but if your thumb is pointed the direction of the magazine tube it works better.
And practice. I'm in the 10 second range for shoot, load 8 off the belt, shoot. After practicing with my 1300, the M2 loading area seems HUGE.
FYI: The shell release is so you can unload the chamber without emptying the whole tube. You can have a full mag, one in the pipe, pull the shell out of the pipe and change it (field to buck, buck to slug). Also, if you modify it slightly you can ghost load it to gain an extra round. 8 in the tube, one on the lifter and one in the pipe for a total of ten.