Well, this is the direction I went for my keggle tops. (Sorry for the blurry photos. I got frustrated trying to focus on shiny metal.)
After I cut the tops off, I ground them down a bit more to remove any sharp edges. Then, I used my lathe to turn handles out of cocobolo (if you're going to be a bear, be a grizzly, right?). Once I was sure it was all going to work out, I bought stainless steel bolts and washers to hold them all together.
I don't expect the need to disassemble them, but I wanted the option. I guess if I drop them and break a handle, it would be nice to be able to replace it without too much difficulty.
I'm considering adding some high-temp silicone to the inside cracks around the washers/nut, to prevent moisture from getting into the space under the handle. Speaking of that space, I was initially concerned about that space getting really hot and bursting. The more I thought about it, though, it seems unlikely for several reasons. Mainly, the max temp would be 210. It's not like the 'exploding kegs' experienced when moisture gets trapped in the rolled edge of a keggle and it is heated with direct burners. (If you don't know what I'm talking about, look it up or at least make sure you have small holes drilled in the lower rolled steel edge of your keggles--the part that touches the ground.)
Back to my lids. I used SS washers up top to expand them enough to overlap the hole in my keg. Each was drilled on a drill press while I held it with a pair of pliers.
You can also clamp them in a vise and drill sideways but that's how I drilled the small washers and it was a pain. I used a rivet gun from Harbor Freight to snap them together.
A note on my Harbor Freight experience: I bought the yellow one for $4.99. On the 4th (of 12 for two lids) rivet, the extra piece that gets ejected stayed lodged in the tool. No matter how hard I pulled/pried/oiled/etc, it was there to stay. I bought another one and the same thing happened on the SECOND rivet. I talked to one of the employees and he exchanged both of the $4.99's for the $9.47 model and gave me back my change--awesome... I used it in the store and it had NO problem with the remainder of both lids.