iOS modal UIViewController that doesnt cover all screen

i need a parent view controller to load a modal view controller, such that only the bottom of the screen is covered by the modal's view. with the normal invocation, the modal's view is resized to be as high as the screen (460px) and slides all the way to the top. i tried forcing the size and the y origin back to what i need in viewDidLoad and viewWillAppear: with no effect. if i force the origin in viewDidAppear: (which is not really desirable - it's too late by then) the view does come back to where i want it, but instead of the parent's view contents that i want on top, i get the contents of whatever would be underneath that parent's view. how would i do that? it should be simple, but i guess i'm missing something...

to make it easier, imagine that what i want to achieve is a UIActionSheet, except that it has my own contents, not just a few buttons.

thanks.

thats kind of how i have it right now - i instantiate the view controller then add its subview to the current view. problem is that the view controller that would want the modal is actually part of a tab bar controller, and the tab bar still remains displayed at the bottom. tapping on the tab bar is still possible, obviously screws up everything, and this setup doesnt look modal at all...

i'll keep wrestling it and let you guys know if i found a solution.