Hi,
I am updating this post according our e-mail conversation in case somebody else is interested.
I would rather use static HTML web part where you just need to set the text property. Or use some other control - text area, default ASP.Net.
In editable region you need to use LoadContent or SaveContent methods (both with the page info parameter) to load the value to the editable region. I think this may be even worse that one more call through macro or calling the service.
However, this
blog post may give you more details and ideas.
Best regards,
Juraj Ondrus