Unfortunately
FOWI won't work if the Watcher is in play already, since that's definitely an effect "triggered" when a minion is played. I'll let you guys know though if the resident rules guru axes the SP idea.
Threat generation can be handled by
Captured by the Ring,
FOWI (just play Gollum before the Watcher), and even
City Gates. Extending the Gollum package further,
Led Astray adds additional twilight and can replay sites like
Cavern Entrance for multiple swarm attempts.
But right, it does depend on how well the FP can cycle to assemble these cards. It might be more trouble than it's worth. There is an
HKotN /
Leaving Forever loop to draw your entire deck if you wanted, but that Elf is expensive and I guess kind of cheesy.