This is the quickest way I've found without doing any subclasses:
UIView *spacerView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)];
[textfield setLeftViewMode:UITextFieldViewModeAlways];
[textfield setLeftView:spacerView];
In Swift:
let spacerView = UIView(frame:CGRect(x:0, y:0, width:10, height:10))
textField.leftViewMode = UITextFieldViewMode.Always
textField.leftView = spacerView
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