Recently I discovered some short solution for ignoring a single hidden element with the nth-child selector. If you struggle with the same problem the following might be useful:

This is the HTML:

a
b
c
d
e

The following CSS adds a margin right to every second visible element no matter which element has the cpw class.

.cpw {
    display:none;
}

.video_prewrap {
    margin-right:20px;
}

.video_prewrap:nth-child(2n) {
    margin-right:0;
}

.cpw ~ .video_prewrap:nth-child(2n) {
    margin-right:20px;
}

.cpw ~ .video_prewrap:nth-child(2n-1) {
    margin-right:0;
}