Host Silverlight in IFrame & Enterprise Mode

I need to display some legacy Silverlight (OHH-YEAAH!) widgets on a modern website.

Using Edge77 + Enterprise Mode Site List it is possible to force specific sites into IE Mode.

However, I have trouble getting this to work within an IFrame:

Basically I want to do something like this:

<div>

   Chrome Mode

   // IE-MODE
  <iframe src="https://www.silverlight-legacy.com" width="640" height="480">
  </iframe>

   Chrome Mode
</div>

Any advice how to get this working?