Since I have Sony's Sound Forge, I also have the CD Architect program that comes with it, and that allows for all kinds of customization of track gaps. But Sound Forge is kind of expensive, I don't know if you want to buy it just for the CD program. I can get some kinds of customization with Nero, but it takes a lot more fiddling than with CD Architect.
But since there are a few different ways to have hidden tracks, maybe you could describe exactly what kind of hidden track you want to make?
If your Express Burn program can read .CUE files, you might be able to create your custom lengths by hand, by carefully editing that file.