Ffplay, YUV overlays, and SDL_Surfaces

What’s the best way to display an SDL_Surface over a YUV overlay being
used to display an ffmpeg decoded video? Reading through ffplay.c, they
seem to convert subtitle images from RGB -> YUV, and then copy them into
each frame.

Is there a better way? I can use SDL_BlitSurface to copy my surface onto
the screen surface, but the delay between calling SDL_DisplayYUVOverlay
and doing this is enough to cause significant flicker.