So. It’s been a while. I think I’ve found the easier way to trigger a siege, but it would be highly luck dependent. To start; you would need a world with 3 key features:

1. A necromancer tower, complete with necromancy book (this ensures your dwarves cannot die and has a wealth tier high enough to warrant a goblin siege).
2. A nearby goblin pit for easy goblin aggression.
3. Any non-dwarf outpost/town to raid for further artefacts. A combination of these three may just be enough to achieve a Goblin siege in under 2/3 hours - combined with max strength/wrestler dwarves, you could easily defeat all the goblins in a siege.