i havent ried this idea but.....some say to use tape (packing, scotch etc) on the back of the unit to pull hairs and thin it...i'd say go slow..do a little bit..wash wear..wait...if it needs more do more...
personally what i did was rubbing my hand across the back (like smearing something) to thin it out...worked well for me...

here the link for nair....take hersutes advice with that..

http://www.youtube.com/watch?v=rPULkcyVD2Y