How can I specify the vertical alignement of UILabel ?

Hi,
I am using the awesome UILabel-FormattedText extension to set differents sizes of text in one label.
However, I did not manage to solve the problem of vertical alignment.

When I put a 24.0 pt word and a 12.0 pt word side by side, I wish they will be center aligned. But they are bottom aligned. 

Do you have any idea to help me ?

Thanks a lot.
