We did this on a site, and what we did was put the grid in vertical rows.
Example:
<div class="row">
<div class="col-lg-4">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
</div>
<div class="col-lg-4">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
</div>
<div class="col-lg-4">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
</div>
<div>