Is it possible to get the this that a function's caller was called with in JavaScript without passing this to the arguments in a way which supports IE as well as Firefox/Chrome et al?

For example:

var ob = {
    callme: function() {
        doSomething()
    }
}

function doSomething() {
    alert(doSomething.caller.this === ob) // how can I make this work?
}
ob.callme()

I'm starting to suspect it's not, but I thought I may as well ask as it'd make my code much shorter and easier to read.

Thanks for any information!