Random thought on how Steamflogger Boss could work.
Rigger creatures can assemble a Contraption by exiling any number of "Component" artifacts that says that the assembled Contraption will have certain qualities and/or any number of Contraptions, and then put a Contraption token onto the battlefield with those qualities. Maybe to make things easier, Contraptions all start as 0/0 creatures. The key is why the creature is doing the assembling and not the player. And the solution is, the Rigger adds its own qualities to the assembled Contraption.
Like a component would be:
"This Contraption has +1/+1."
A rigger's assemble ability could be:
1R, Tap: This creature assembles a Contraption (Exile any number of Component or Contraption artifacts you control: Put a 0/0 artifact Contraption creature onto the battlefield with the text of the exiled artifacts.)
Contraptions assembled by this creature gain "This Contraption has +1/+0".
Although that last part, with the Rigger adding qualities, does have big memory issues. The fact that you exile Components should make building Contraptions using those easier to keep track of, though. Maybe Riggers just provide "until end of turn" effects.