I haven't worked with any Bucky skeletons, but when I made my cauldron creep, I had to bend the fingers of a Barney skeleton. The Barney hands are solid plastic, and cast as a single piece. I'm not exactly sure if the Bucky hands are the same, but here's what I did.
First, I got a hacksaw blade, a bucket of cold water, and a votive candle.
I worked on one finger at a time, one knuckle at a time, starting with the outermost knuckle and worked my way in. Using the hacksaw blade, I carefully sawed about 1/4th of the way through the first knuckle from the top, them the same from the bottom. Next was the tricky part. I lit the votive candle, and held the hand with that knuckle about 2 to 3 inches above the flame to soften it, then bend it to the position I wanted. Then, holding it in that position, I dipped it into the bucket to harden it, then started on the next knuckle on the same finger.
This method was time consuming, but with a little patience, I got good results.
If you use this method, be aware that this plastic is flammable, and will catch fire very easily. When you're holding it over the flame, pay attention; if it catches fire, blow it out right away (this probably happened to me at least 50 times). After the knuckle heats for 20 or 30 seconds, it should bend a little. Bend it as much as you can (NOT forcefully), and hold that position as you heat it some more. You'll have to do this several times (or more) for each knuckle. In other words, heat it some, bend a little, heat some more, bend some more, etc. until it's in the position you want.
Also, be extra careful not to cut too deep into any of the knuckles. If you do, it could weaken it greatly, or even break off while you're trying to bend it.
I used very fine wire to make the bucky hands grasp the telescope for our crow's nest pirate. It should work for a sword or other object. To stiffen the arm into position, I applied hot melt glue, building up layers in the joints. This held it's position outside for a month in October, then again for a month outdoors when the Bucky was repurposed for our toxic victim the following year. The Bucky in the toxic drum is the same Bucky from the pirate scene.