Sure........you can do it, BUT it won't work well. The reason is sound output devices, like radios, CD players, etc., are impedance matched. When you hook two separate channels to one speaker it screws up the impedance (AC resistance) matching. In addition if your four channel output is four channel stereo, things really get messed up!
Just pick one set of channel wires up to one speaker (temporarily) and try it to see if the sound is acceptable. If not, try another pairing.