What version of Windows are you using? iTunes doesn't have the ability to regulate the balance, but you could use the balance controls for your speakers. You'd have to adjust it to balance left for these songs, then adjust it back to balanced for the rest of the world.
In Windows 7, right click on the sound icon and select Playback Devices. Select the relevant playback device and click on the Properties button. In the Levels tab, you can decouple left and right volume.