I think i found a solution or at least a workaround.
Use an <a href=""></a> as a transparent layer with href and define width, height and z-index.
This works only for html5 banners with only one link.
For example:
HTML Banner:
<div style="position: relative;">
<a target="_blank" href="{your banner click href here}" style="position:absolute; top:0; left:0; display:inline-block; width:300px; height:600px; z-index:10;"> </a>
<iframe src="{put your iframe url here}" width="300" height="600" frameborder="0"></iframe>
</div>
Remember to use the same width and height in a href style and in iframe.
Best regards