I would like to post something which includes Greek alphabetical characters.

[usonian]

7. I asked for Greek.

For non-rendering characters, images will have to do for now.

In the old days, math editors would export images of typeset math equations, loaded with Greek characters, as an image you pasted into your word processor document. May still do, I don't know.

Alternatively, type or hand write the text and take a photo or screenshot of it to upload.