Help me bottom align these panels

Tops of A and C. Bottoms of B and C. Without flexbox, javascript, or breaking responsiveness!

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
<div class="container-fluid">
  <div class="row" id="toprow">
  
      
    
    <div class="col-xs-9 panelab">
      <div class="panel panel-default">
        <div class="panel-heading">Panel A</div>
        <div class="panel-body">
          <div class="row">
            <div class="col-xs-4">
              <img class="img-responsive img-rounded center-block img-thumbnail" src="http://placehold.it/320x240">
            </div>

            <div class="col-xs-4">
              <img class="img-responsive img-rounded center-block img-thumbnail" src="http://placehold.it/320x240">
            </div>
            <div class="col-xs-4">
              <img class="img-responsive img-rounded center-block img-thumbnail" src="http://placehold.it/320x240">
            </div>
          </div>
        </div>
      </div>
      <div class="panel panel-default">
        <div class="panel-heading">Panel B</div>
        <div class="panel-body">
          <div class="row">
            <div class="col-xs-2"><img class="img-responsive img-rounded img-thumbnail center-block" src="http://placehold.it/320x240"></div>
            <div class="col-xs-2"><img class="img-responsive img-rounded img-thumbnail center-block" src="http://placehold.it/320x240"></div>
            <div class="col-xs-2"><img class="img-responsive img-rounded img-thumbnail center-block" src="http://placehold.it/320x240"></div>
            <div class="col-xs-2"><img class="img-responsive img-rounded img-thumbnail center-block" src="http://placehold.it/320x240"></div>
            <div class="col-xs-2"><img class="img-responsive img-rounded img-thumbnail center-block" src="http://placehold.it/320x240"></div>
            <div class="col-xs-2"><img class="img-responsive img-rounded img-thumbnail center-block"...

CSS

#toprow {
  background-color: lightblue;
  overflow:hidden;
}
#toprow .panelc, #toprow .panelab {
  margin-bottom: -99999px;
  padding-bottom: 99999px;
  float:left;
  position:relative;
  
}
.panelc {
  background-color: #ff0000;
}
.panelab {
  background-color: #00ff00;
}