Here's an idea I picked up off the forums (maybe from Girlinhat?). I set up two magma forges, with one set so only those above novice can use it, and one set so only dabblers can use it. The dabbler forge is loaded up with 10 orders for copper bolts, all on repeat (this assumes I have lots of copper ore handy, which is usually the case). Then I take a bunch of otherwise unremarkable dwarves who don't have any moodable skills (haulers and cheesmakers and soldiers who have no other skills) and turn on weaponsmithing for all of them. When they have free time they'll head down to the forge a make low quality bolts (perfect for target use) and build up just a bit of weaponsmithing skill. when they get up to novice I turn the skill off (if I happen to notice - it's not a big deal either way since novices aren't allowed on either forge).
So if any of those dwarves gets hit with a non-possession/fell/macabre mood, they'll make a weapon and I'll have an instant legendary weaponsmith.
It's only practical if you have magma forges and an abundance of a weapon-grade material like copper or silver (or even iron if you want to divert some from steelmaking). But every fort has magma if you're willing to put in a minimal amount of effort, and it's rare to have a fort without a bunch of tetrahedrite or galena.
I don't think that it's really practical, and it doesn't really save you a lot of metal, depending on how many dwarves is a "bunch" (if it's equal to the amount of unarmed dwarves that is needed to kill a single badger, it'll be quite a big bunch
).
Consider that a mood bumps a skill to about Legendary+1, which is 20000 experience. If you train a dwarf from Dabbling, you only need 333 bars of metal. Since Novice requires only 500 experience (8 metal bars), you need to do it with much less then 41 dwarves to make it worth it (say, a "bunch" is 20 then, and needs 160 metal bars, for exactly half the cost of training from scratch).
Then you have the random chance that may or may not pick one of these 20 dwarves on the rare fey mood occasions (some of which will be possessions).
If you get a Weaponsmith migrant (pretty common), you have wasted a lot of metal, because he'll need even less effort to train.
So if you have plenty of useless metal (which is the case on most maps), you're better off just making a bunch of weapons with one dwarf (I'd recommend copper crossbows, since you'll get a lot of masterpieces very soon, which are actually useful). And if metal is very scarce, by the time you need a good Weaponsmith you'll probably melt enough goblinite to get 333 bars or whatever is needed to train the highest migrant Weaponsmith that you'll inevitably receive at that point.