I contacted Optimizelys support team and got the following answer if anyone else is interested:
I have contacted our development team regarding your question and unfortunately it seems like this is not supported. Please see the response from our developers below.
"Unfortunately It is not supported to do that."
Our customer want's to know if it's possible to drag a block from the TinyMCE editor to a content area?
There's support to do it the other way around (drag a block from the content area to an editor).
Is this by design?