Here's an ePub showing both float left and right.
I use spans in the paragraph but they are both defined before the text of the paragraph, (otherwise they don't float properly.) Works with my Sony reader which is ADE based. (I think this is really the same as mzmm's solution, but I prefer using span.)
.cen { text-align:center }
.fll { float:left }
.flr { float:right }
<p class="cen"><span class="fll">1</span><span class="flr">1</span>Text</p>