Originally Posted by Analog
It also might (theoretically), be possible to just take off the cogs from your existing freewheel (minus one), depending on the kind of freewheel it is.
I've never actually tried this, but I can't see any reason why it wouldn't work.
because it's a freewheel, and it's all one piece. (you are right, if it were a cassette, but you'd still need spacers)