Switching background in markdown beamer

I'm trying to transfer a LaTeX/LyX presentation into a Beamer markdown document.

On some slides I suspend the background image (which has logos of funding bodies on it) to make more space for code output.

I previously did this with the following command:

\bgroup
\usebackgroundtemplate{\includegraphics[width=\paperwidth]{background.png}}
\begin{frame}[plain]
Some text here!}
\end{frame}
\egroup

I have tried something like this (which doesn't work):

\bgroup
\pgfdeclareimage[width=\paperwidth]{empty}{Template_blank.png}
\usebackgroundtemplate{\pgfuseimage{empty}}

## New Slide

some text
\egroup

Any ideas?