Even if the answer is a bit late, I came across the same problem and to the conclusion that this is at the moment still not possible.
There was, however, a feature request opened a while ago here. I think the most you can do is to upvote the issue.
Embed without executing
There is a half-functioning workaround though...
You can export your already executed notebook as a gist and embed this into your webpage.
- Save Colab as a Gist (Colab -> File -> Save a copy as Github Gist)
- Make the Gist public (Gist -> Edit -> Make public)
- Embed the link into your webpage
For further instructions, details and screenshots see this article.