I'm suggesting to install a 'Usergroup-Based Blocking' system - might not make sense, cause I'm not sure what it's called.
For example, I could put this in my thread.
[block=leecher]
text1
[/block]
And the 'text1' would be visible to everyone except leechers, to which it would display a 'Your rank is not high enough to view this message.' error over just that block of text.
And you could enter any variety of rank, such as contributer, donator, elite, ect.
Just an idea.