I think they are legal in WA.  We used to use them years ago in Puget Sound when trolling three rigs (two on down riggers and one on a weight release).  I never liked them because of the loss of the lead (which are not cheap anymore!).  Haven't used one in years, but still think you could if you wanted to. 

A 3# cannonball goes for, what ? $10-12 a piece ? Yikes.

I mean, its one thing to get snagged up and lose a $3 ball and a $15 flasher, but this is going in expecting to dump the tackle.

Doc Thoke has diagram in his book of making a rock release.  Hell, just use a Delta Diver, or Deep Six, the rock makes a lot of drag compared to lead.