You can use the solution described here:
http://blog.vjeux.com/2011/css/css-one-line-justify.html
This will justify a single line but adds a space after, so if you know the height, you can specify it with overflow:hidden to conceal it and still get the justification.
.fulljustify {
text-align:justify;
}
.fulljustify:after {
content: "";
display: inline-block;
width: 100%;
}
#tagline {
height: 80px;
overflow: hidden;
line-height: 80px; /* vert-center */
}<p id="tagline" class="fulljustify">Blah blah blah</p>