how to override the subtitleoverlay bin in playbin2

[bcxa sz]

Hi Developers,

I have developed own text overlay element to match my embedded system.
And also due to some reason (S/W and H/W architecture), I can not
insert the ffmpegcolorspace (pre-colorspace) after my video decoder
element.

And I found that the gstreamer native subtitleoverlay bin is hard
coded to use gstreamer native text overlay element and insert
pre-colorspace converter. And playsink bin in playbin2 is also hard
coded to use gstreamer native subtitleoverlay bin.

So I WANT TO KNOW whether it is possible to override the gstreamer
native subtitleoverlay bin in playbin2 with my own developed
subtitleoverlay bin which can use my own textoverlay element.

best regards

BCXA