I get my legs round again like
@SixZeroFour says.
Then, I cut 2 or 3 inch long (just a little longer than the leg socket is deep) pieces of electrical conduit (I think it's 3/4 inch) to insert inside the leg. Before inserting, I use my bench grinder to grind a strip of the metal away. The leg won't go into the socket with the conduit in it unless you grind this strip. Once the strip is ground, you need to be sure you have the strip lined up in the leg with the dimple that holds the leg in. Once you have the leg with insert ready to install, it's a good idea to lube the leg and socket (I use a silicone spray), line the leg up correctly, and push/wiggle the leg in.
Note to any considering this: It's kind of permanent and you may not be able to get the leg out again, but this fix sure as hell keeps the legs in tight and the kettle stable.