I'll throw in my vote for JB weld too. I had 1/8" cracks on each spoke plus lots of other smaller ones. I ground them out a bit, filled them, wrapped them with tape to keep the runny JB weld from dripping out, then sanded away. I used files for the heavy excess removal.
Of note, I painted the wheel with 2 part black gloss paint from NAPA. The wheel still had hairline cracks, but I wasn't going to bother with every single crack. Those hairlines show through, but it's not a big deal and it looks darn good.