lavpipe should execute the command lines in the pipe list files through /bin/sh instead of exec. That would allow the commands to themselves be pipelines, which is needed for commands like "/bin/ls frame*.jpg | jpeg2yuv ..." or "lav2yuv foo.avi | yuvfps ..."
work around is to create a shell script with the desired pipeline - the script would be exec'd by lavpipe. In any event nothing's going to be done I'm afraid unless new developer(s) are found.