The only way I can think of is by using the Iframe component which loads a html page, but I wouldn't recommend it.
The iframe actually floats over your flex application and is a seperate div in your html template.
Flex is not the best in supporting HTML, so using the TinyMCE right away in your Flex application is impossible afaik.
Any reason for not using the RichTextEditor component? Lack of options?
Yes, I can't use Flex provided Rich text Editor because its only providing text options. I need image options as well. Any third party component that is available in Flex?