Mmm I think there's a company which makes really thin adapters (2mm), I read it somewhere on the net. I'll see if I can dig it up. Otherwise as gbeal mentioned, filterdrawer is the best way to go.
Dimitris, you need a nikon flange to M42/M48 adapter. Like this:
http://www.gamaelectronics.com.au/files/canon%20set.jpg
http://www.teleskop-express.de/shop/...n-Bayonet.html
I got mine from QHY for something like $40