How to Enable Frame Blending in Blender 2.74? I can't find the option that supposedly existed in Blender 2.49: "Enable Frame Blending". Does anyone know where it is, or where is its analog?

I shot a sunset - 30 minute video I want to turn to 10 second sped-up video. I easily do that with Add->Effect Strip->Speed Control, and setting  to 200. 

This drops 199 frames out of 200, which isn't quite what I'm after.

There are people walking in front of the camera. I want to blur every 200 frames into 1, so that there are blurred trails of people rather than snippets of people. 



Google says that all I need to do is check the "Enable Frame Blending" option. However, I cannot find this option in Blender 2.74 UI or source code, so it probably got renamed. Does anyone know how to fix this? I cannot use Blender 2.49 (I tried.. The new blender UI is tough for me to get around, googling basic things 20 minutes at a time; the old blender is however just an impenetrable wall of foreign UI concepts)
This option was lost in the transition to 2.5. Not sure exactly why, maybe the design of it didn't fit with the newer design (under the hood, not UI) It might be a Todo item.
You might want to use the program 'slomovideo' http://slowmovideo.granjow.net/
that does pixel-flo type blurs and blends to do this effect. (It is also free and open source)