How to get (x,y) location of the sub-string from Multiline UILabel text (iPhone SDK) ?

Question

How to get (x,y) location of the sub-string from Multiline UILabel text (iPhone SDK) ?

i.e. :

I am having a multiline label..

Now i want to get origin-location of the substring of UILabel.text?

suppose this is my string displayed in Multiline UILabel :

"KDDI's 'smARt' television viewing concept links phones to consumerism at long last http://bit.ly/ae1FA8"

Now i want to get the starting Location (x,y) (respect to UILabel starting position)of substring "http://bit.ly/ae1FA8".

Is there any way ?