1)Splitter:That's a splitter might work I guess but since your cables are 1/4" ones you'll need adaptors for it unless your splitter is also 1/4".
2)You can use a Mixer, connect 2 inputs into the mixer and send the output into the amp.
3)You can get a Pod X3 Live which allows you 2 connect 2 different instruments with 2 different signal chain.
4)Use your computer speakers?
5)If your amp has a MP3 in, you might be able to use that too. So 1 guitar through the normal input, 1 into the CD/MP3 in.