I've made plenty of stove top cannabis ejuice. My guess would be that sprinkling some kief into a tank would be gross and probably do absolutely nothing except fuck up his coils. The juice I have made was pretty strong, almost like vaping flower, but I was a smoker at the time and I only made it if I was dry.
No, you cannot vape dry herb in your AIO. It was designed for ejuice. You could conceivably look for a 510-threaded flower or oil attachment but I'm pretty sure an AIO doesn't have any wattage adjustment so that probably wouldn't work very well.
A vapcap is $60, just sayin.