I'm not familiar with the limits of the ListView on the compact framework, but on the standard framework, you can use the TreeNode.StateImageIndex property. The unchecked/checked states are in fact using small images embedded in the standard winforms code (If I remember correctly, they are index 1 and 2). So, for example, if you do this:

private void lvMeters_ItemCheck(object sender, ItemCheckEventArgs e)
{
    e.Item.StateImageIndex = 3;
}

It will change the small icon and set it to nothing. You can also use the ListView ImageList.