In Oregon, as in most party-registration states, when you register to vote you also - at the same time - select which party you declare to be a member of, or say you're a member of none. Under the introduced-today Idaho Senate Bill 1198, a response to the closed-primary lawsuit by the Idaho Republican Party, the same idea would apply in Idaho.
Parties would then have the choice of allowing only declared party members, everyone, into their primaries.
The Ballot Access News site has a little more on what's likely ahead: "Voters who choose a Republican ballot in the May 2012 primary would be automatically listed as Republicans, and the same is true for the Democratic, Constitution, and Libertarian Parties. The bill does not provide for a blank line on the voter registration form for anyone to write-in the name of an unqualified party. That aspect of the bill may be unconstitutional; courts in five states have said that voters must be allowed to register into active unqualified parties. Also, the failure of the bill to provide for a blank line for a voter to write-in the name of a newly-qualifying party would mean that if a new party qualifies in Idaho, all the voter registration forms would need to be immediately reprinted."
Something like this is one of the few remaining non-budget, non-fiscal measures awaiting resolution before the Idaho legislature adjourns, which may be in another couple of weeks or so. One way or another, they really do need to respond to the ramifications of the lawsuit.
There is a slim chance otherwise; some reports have surfaced that associated parties in the case (not the Republican Party, which was the successful plaintiff, and not the state, which was the defendant) evidently are seeking an appeal to the 9th Circuit Court of Appeals.