Stroke left and right side of rect svg

It's another hack, but you can add a filter to your shape and clip the top and bottom by your strokewidth - which here I'm assuming is 1 unit.

<defs>
   <filter id="clippy" x="0" y="1" height="248" width="356">
     <feColorMatrix type="identity"/>
   </filter>
</defs>
<rect filter="url(#clippy)" class="extent" width="356" height="250"
      style="cursor: move;opacity: 0.2; fill: #FF9000;" x="578"></rect>

Update:

Here is the d3.js version of the answer created by Christopher Chiche (see original lower down):

svg.append("defs").append("filter")
    .attr("id", "clippy")
    .attr("x", "0")
    .attr("y", "1")
    .attr("height", "248")
    .attr("width" "356")
    .append("feColorMatrix")
    .attr("type", "identity")

svg.append("rect")
    .attr("filter", "url(#clippy)")
    .attr("class", "extent") 
    .attr("style", "cursor:move; opacity:0.2; fill: #FF9000")
    .attr("x", "578")
    .attr("height", "250")
    .attr("width" "356")

Here is the d3.js version of the answer posted by Michael Mullany. If you think of accepting my answer, please accept his instead. I just did this as an exercise to have fun:

svg.append("defs").append("filter")
    .attr("id", "clippy")
    .attr("x", "0")
    .attr("y", "1")
    .attr("height", "248")
    .attr("width" "356")
    .append("feColorMatrix")
    .attr("type", "identity")

svg.append("rect")
    .attr("filter", "url(#clippy)")
    .attr("class", "extent") 
    .attr("style", "cursor:move; opacity:0.2; fill: #FF9000")
    .attr("x", "578")
    .attr("height", "250")
    .attr("width" "356")