Neat idea, but it looks like the math doesn't really work out: https://space.stackexchange.com/questions/66295/is-interstel...

Though it looks like these folks are thinking about blocking from near the star, which requires megastructures for anything detectable. I haven't done even back of the envelope calculations but I'd guess the limiting factor is you'd only be causing an eclipse/transit in an unusably narrow angle directly behind the craft. As you get closer the cone expands but the signal weakens.