Bottomless CRichEditCtrl

I want to create an edit box like the one that listviews use for renaming.
I can't figure out the magic that makes a CRichEditCtrl bottomless.
I have send the the control the message that allows it to respond to the request for resize:
m_pEdit->SendMessage(EM_SETEVENTMASK, 0, EN_REQUESTRESIZE);


I figured that I would want to visit the controls size each keystroke, and send an EN_REQUESTRESIZE message.
However, that message requires a RECT. Where Do I get this from?
Is this the correct approach?
TIA Larry