background-size in Yahoo Mail

Before

<td style="background: url('bg.jpg') center/cover no-repeat;">
  Content
</td>

After

<!--[if gte mso 9]>
<v:rect xmlns:v="urn:schemas-microsoft-com:vml" fill="true"
  stroke="false" style="width:600px; height:400px;">
  <v:fill type="frame" src="bg.jpg" />
  <v:textbox inset="0,0,0,0">
<![endif]-->
<td style="background: url('bg.jpg') center/cover no-repeat;
            background-color: #333;">
  Content
</td>
<!--[if gte mso 9]>
  </v:textbox>
</v:rect>
<![endif]-->