Climbing bleachers, jogging, walking, hiking, working with weights, training with loaded backpacks, they all help build stamina and cardio-vascular health. The better health you're in the better off you'll be.
However, I cannot comment on the snorkle idea.
I do believe a body has to acclimate to the altitude, being in good cardio shape with decent muscle tone helps to acclimate quicker perhaps, as your body us more efficient at utilizing the O2 if you are in shape. If you're out of shape and struggling just to climb or whatever, the the effects of the altitude will be exacerbated.
But I believe there is no substitute for being there. It is something your body just has to do. You're dealing with lower oxygen levels, air pressure changes, dryer air, etc.
I'm pretty sure it is safe to say there is no real way to acclimate your body to the effects of high altitude other than being at high altitude. I've made numerous trips to Colorado skiing and this has been my experience.
If there is a way, I'd like to know it.
