streaming – ffmpeg dash output for multiple resolutions to be in the same mpd file

I am using ffmpeg to convert an input stream into multiple resolutions and creating an mpd for each resolution.
So far, so good.
But I am trying to find a way to create a single mpd for all resolutions. This will reduce a lot of pain for me, downstream.
Is there an option available for this in ffmpeg natively or should I look at ways to merge mpd files ?

This is how my script looks so far. Please do the needful.

"ffmpeg -f avfoundation -framerate 30 -i 0:0 -filter_complex '[0:v]split=3[out1][out2][out3]' \ -map '[out1]' -s 1280x720 -vcodec libx264 -single_file 1 -f dash /path/to/720.mpd \  -map '[out2]' -s 854x480  -vcodec libx264 -single_file 1 -f dash /path/to/480.mpd \  -map '[out3]' -s 640x360  -vcodec libx264 -single_file 1 -f dash /path/to/360.mpd"