Aw, when my lenses get dusty I just throw 'em away.
Seriously, a funny aside. When I was a kid, a (now famous) photographer showed me how to clean a lens by first taking a swig of whiskey, then 'hush' a breath to fog the surface before wiping it. Really, I think he was just trying to freak me out. When I tried it on my (plastic) lens, I got sick ... it gets worse, so I'll stop here.