What your looking to do is to condition your shins right, the best way ive found that effectively conditions shins is to take a wooden stick and continually smashing it on your shins, the bottle method works too but id rather condition it the painfull way rather than the easy way, the easy way dosent always prove to be 100% effective
Well I plan on using a heavy bag soon, but I was just looking for a substitute until I have one available. I was thinking using that using shin guards against a tree(with the hard part removed, leaving a somewhat thick cushion) would be similar to kicking a slightly cushioned heavy bag.
Also, I've read that using the bottle method/other similar methods only deadens nerves, but doesn't actual strengthen shins. I'm looking for ways to actually strengthen my shins, not just to remove pain from them.