Thats how high I often hunt, mainly because I like it, I love climbing as high as possible, deer never notice me, and it has never wrecked a shot opportunity for me. I only climb that high when it works out though, like in a stand of oaks or something, if it is not resonable to climb that high or if it is going to hinder my view at all, I stay lower, 20' or so.
ANyways, to the question, the only way to really avoide the problem is to tighten the strap up as much as you can at the bottom of the tree so the stand is leaning way up, don't get it too tight that you can't even get your feet in it or climb with it, but get it as tight as it will allow you to, then as you get higher on the tree it will level out. It is always good to practice climbing a particular tree before you hunt it so you know what to expect when you climb it. Some trees just taper too much and you won't get enough adjustmen out of your stand to sit properly, so you may just have to find a different tree or not climb as high.

There has been a few times when I did what rile1564 is talking about, had to tighten the strap up in the tree. It works with some climbers, but not with others. It it pretty much impossible to tighten up the lower platrform on my Lone wolf hanc-climb combo.
I know I am going to get barked at, but I have never worn a safety strap in a tree. I know I should, and I would like to, but I can never find a good strap, or they seem to get in the way or are a pain to put on. I should prebobly start one of these years though before it is too late.