I've done this a few times, so I'll tell you what has worked for me.
For catching it you'll want to dig a 1 tile wide tunnel connecting the caverns to your fortress. Choose a location in that tunnel where you want to trap it, at least 2 tiles in length, and install doors at its entrance and exit. On the outside of those doors you should build 2 raising bridges and link them to levers. Now would also be a good time to carve fortifications and build the rest of your web farm. If you try to build it after trapping the FB your workers will be constantly terrified and tangled in webs. The tunnel should look something like:
REST OF
WEB FARM
=======###========
>>D D<<
==================
where = are walls, D are doors, >> are bridges raising in the direction of the arrows, and # are fortifications.
Give the FB a clear path into your fortress and wait for it to run into the tunnel. Note that, despite being building destroyers, FBs can still refuse to path into your fortress if there are any locked doors or other obstacles in the way (they may, on occasion, refuse to move even if they do have a clear path). Once the FB is between the two doors, simply lock them. That will give your dwarves plenty of time to pull the lever, raising the bridges and sealing the trap.
For bait I recommend using either captive werebeasts or undead. Werebeasts may stop working once they go insane, unless they go berserk in which case you're in luck. Small undead (eg. cats) can get killed by flying webs, but larger undead make perfect bait. Captive invaders may also work, although I haven't done extensive testing on those. If you're feeling really dwarfy you could use a second FB as bait, since they're always hostile to each other.
If you're building a silk farm it's relatively easy to make it double as a trap for caging any non-webbing trapavoid enemies. I usually start a FB zoo as a side project once I've got my silk farm running. It's also possible to use multiple layers of carefully arranged retracting bridges to act as stochastic conveyor belts, spreading the webs out and letting you cover a larger number of traps. I can post my designs for those systems if you're interested.