Converting my SD card to dual boot (w/ Retropie)

I have installed OSMC to use my Pi as a mediacender.

However, I’d very much like to play classic games (Mame!!) w/ [Retropie] (The RetroPie Project - petrockblock). There fore I need to dual boot my Pi. That’s not a problem if you start from scratch. There are tools to make a dual boot SD card and to install multiple operating systems on your Pi (i.e. my beloved OSMC and Retropie). But I do not want to start from scratch. I want to keep the add-os and configuratin of my OSMC installation the way it is right now. So I’m wondering if there’s any way to “disc clone” my current OSMC SD card to a dual boot card. That is: make a dual boot SD card myself by using standard Linux tools like dd etc.

There is no need of dual boot. You can check this implementation