Unfortunately they use different IDs on the profile view (web page) and the embed iframe, so I can't easily make a translation like the youtube one. What you can do in forums that have HTML enabled (usually the members-only ones, not the publicly available ones) is post the iframe link as plain text and click the "Enable HTML" checkbox in the lower left.
Example in Backwash, which allows HTML:
http://sonsofsamhorn.net/topic/52350-test/?p=5591734
EDIT: Hmm, that checkbox isn't there when initially posting, only when editing a post. You'll need to either edit your post, or use the full editor ("More Reply Options" button from the quick post box) and click "Enable HTML" which is over to the right on the full editor: