Um, i'd still recommend buying the tool... Even if you were going to cut the plates on one link, you'd still have to press the pin out.

I suppose you could lay the bike on the side, set up 2 wood blocks under the chain, leave a small gap between them, then use a center punch and hammer to bang out the first pin...

On the other hand, if you don't already have a small mutlitool for your bike (every cyclist should have a small multitool), there are afew that come with a chain breaking tool which is more than enough for removing/installing the occasional chain pin.