In your Admin Area there is a setting that allows the redirect to cart to be turned off.
You can try that, it still refreshes but stays on the page the buy button is on.
As an alternative, as @Tsimi rightly says, you could try Ajax.
I experimented with something, you can try it http://template.me.uk/234bs3/index.php - this is just to prove it is do-able, it is not currently available as an addon.