A couple years old, but here is a rundown on computer-oriented Japanese TV remote access options.
Update from October 2011 regarding iOS viability. Looks like a subset of Japanese broadcasters publish rtsp:// streams.
The site is emphatically not about baseball though, so I am somewhat dubious if the various yakyu providers expose their programming in such a manner. It would be really cool if they did, though. One thing I noticed last year was that sometimes there were multiple competing broadcasts of the same game, and the relay originator would switch between them occasionally, like if an ad came on.
One of these channels appeared to specialize in non-commented broadcasts, so that the game would play without any narration or commentary, just with the sound of the park and the game itself. I really liked that.
It seems like someone this year mentioned that that may be an option on HD sports broadcasts in general, a setting that the viewer can select.