How to change a span to look like a pre with CSS?

Look at the W3C CSS2.1 Default Style Sheet or the CSS2.2 Working Draft. Copy all the settings for PRE and put them into your own class.

pre {
    display: block;
    unicode-bidi: embed;
    font-family: monospace;
    white-space: pre;
}

See the white-space CSS property.

.like-pre { white-space: pre; }