[Someone]

If you cheat, that’s trivial.

Start with the target stable state, and add something that, on its own, dies out, far enough from the target stable state to not interfere with it.

You could cheat a tiny bit less by removing a small stable part from the ‘edge’ of the target pattern, firing gliders at it that, just before hitting the smaller target, collide to complete the stable pattern.

I think you can generate many stable patterns by taking this to the extreme: start with an empty target area, and fire gliders at it that collide and add stable parts one by one.

You may need lots of gliders, but since the board is infinite, it’s easy to prevent the separate glider groups from interfering with each other.

[egypturnash]

Dense grid of traffic-light oscillators would work too, it wouldn't move across the board.

So could a bunch of beehives/loafs/etc.