What is the best way to position a view relative to the size of its superview, when the bounds of the superview are not yet known?

I am trying to avoid hard-coding coordinates if it is at all possible. Perhaps this is silly, and if so, that's a perfectly acceptable answer.

I've run into this many times when working with custom UI. The most recent example is that I'm trying to replace the UINavigationItem plain-text title with a custom view. I want that view to fill the superview, but in addition, I want a UIActivityIndicatorView on the right side, inset about 2 pixels and centered vertically. Here's the code:

- (void) viewDidLoad
{
    [super viewDidLoad];

    customTitleView = [[UIView alloc] initWithFrame:CGRectZero];
    customTitleView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;

    titleLabel = [[UILabel alloc] initWithFrame:CGRectZero];
    titleLabel.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    titleLabel.lineBreakMode = UILineBreakModeWordWrap;
    titleLabel.numberOfLines = 2;
    titleLabel.minimumFontSize = 11.0;
    titleLabel.font = [UIFont systemFontOfSize:17.0];
    titleLabel.adjustsFontSizeToFitWidth = YES;
    [customTitleView addSubview:titleLabel];

    spinnerView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
    spinnerView.center = CGPointMake(customTitleView.bounds.size.width - (spinnerView.bounds.size.width / 2) - 2,
                                     customTitleView.bounds.size.height / 2);
    spinnerView.hidesWhenStopped = YES;
    [customTitleView addSubview:spinnerView];

    self.navigationItem.titleView = customTitleView;
    [customTitleView release];
}

Here's my problem: at the time that this code runs, customTitleView.bounds is still zeroes. The auto-resizing mask hasn't had a chance to do its thing yet, but I very much want those values so that I can compute the relative positions of other sub-views (here, the activity indicator).

Is this possible without being ugly?