I use the stepping when I'm watching tv but found the height stopped challenging me. A few plastic steps we could stack under the wii fit would be great. I'm using a foam stepper block at the moment to give me the challenge I desire but it's just not sturdy, lol. I'd fuss at my kids for using it.
Elcomer

There are a few specially build products for lifting the Wii Balance Board up for more exercise. One in called the Riiser, which you can find on amazon for about $20.

That might be a bit studier

I use my step while doing running. that is one way to do step arobics with the wii.

Everlast makes a riser set for the Wii Fit Board.

I have the lumber and tools around to build a platform. I realize not everyone does. So, would a set of bed risers do the trick for you?