The Parties, or a party, could set a date for primaries in all states and
bar it's candidates from running in earlier ones.
Of course that'd be 'too easy'.
You're right about the problem. Maine and Iowa are not bellwethers of any sort.
You are right that the national Parties could do this, if they wanted to. But the national parties are run by the same people who led the Parties in Congress. For the same reason that Congress won't act, the Parties won't act.
So, this will only happen if common sense rears its ugly head in the state legislatures, it can be done. And to my experience, the state legislators are common sense folks.
Billybob