cheap/easy way to amplify sound over the holidays without actually buying an amp?

Over Christmas there will be lots of sharing of my ekit with fam. We plan on playing lots of CloneHero and I'd like it to be enjoyable for an audience to watch and hear how well others do playing along with songs etc.

I normally play with headphones to get fully immersed and I'm not really set up for others to hear the kit or the songs being played on it.

I'm thinking of splitting the headphone out cable to an additional (and likely temporary) speaker so an audience could hear the performance but I have no idea what sort of speaker would even be passable for this use over a proper wedge amp or something ..any ideas or things you've tried that might be passable to use over the holidays?