[O] org-beamer: How to leave a block?

[Florian Lindner]

Hello,

I have

*** MATLAB vs. PETSc                                                :B_quote:
:PROPERTIES:
:BEAMER_env: quote
:END:
some lengthy quote

from the manual

Now I want to put the "from the manual" below the quote environment, not 
inside, like that:

\begin{frame}
\begin{quote} %% MATLAB vs. PETSc
some lengthy quote
\end{quote}
from the manual
\end{frame}

How can I achieve that which org-mode beamer, i.e. leave a block?

Thanks,
Florian