Following Mike's advice, here is what I did.
In tableView:cellForRowAtIndexPath:
...
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
// Drawing our own separatorLine here because I need to turn it off for the
// last row. I can only do that on the tableView and on on specific cells.
// The y position below has to be 1 less than the cell height to keep it from
// disappearing when the tableView is scrolled.
UIImageView *separatorLine = [[UIImageView alloc] initWithFrame:CGRectMake(0.0f, cell.frame.size.height - 1.0f, cell.frame.size.width, 1.0f)];
separatorLine.image = [[UIImage imageNamed:@"grayDot"] stretchableImageWithLeftCapWidth:1 topCapHeight:0];
separatorLine.tag = 4;
[cell.contentView addSubview:separatorLine];
[separatorLine release];
}
// Setup default cell setttings.
...
UIImageView *separatorLine = (UIImageView *)[cell viewWithTag:4];
separatorLine.hidden = NO;
...
// In the cell I want to hide the line, I just hide it.
seperatorLine.hidden = YES;
...
In viewDidLoad:
self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;