First, if your dog has a sensitive stomach, maybe start by only introducing one treat at a time so that you know which one is the problem.
For a sensitive dog, I would also introduce new foods slowly - start by testing it using one or two pieces in a regular training session at home. That way you can give her tummy time to learn to tolerate it instead of being assaulted with a new, probably very rich, food. Heck, even my dogs - who have generally iron clad stomachs - get an upset tummy if I give them too much of a new thing all at once, especially if it is something fatty or high in salt (like hot dogs and cheese). By using "problematic" treats more frequently but in smaller amounts, I have found that they are able to tolerate things that caused issues when initially introduced in large quantities in a session fed too much in one session. For example, the first time my youngest dog got chicken hearts as a treat, she got over a dozen of them and later had diarrhea. She is only 11lbs, so a dozen chicken hearts is a lot! So I started using them in more limited quantities - 1-2 cut up hearts (cut into 4-8 pieces per heart) per training session, a few times a week, and gradually increased the amount. Now she can eat an entire 1/2 cup container full with no deleterious effects.... except maybe getting pudgy, lol. (This is just an illustration that dogs can come to tolerate foods if they are introduced slowly - obviously if your dog is allergic to chicken, don't use chicken hearts!)
Maybe put a handful of his kibble in a baggie, toss in a few pieces of hot dog, and let it "marinate" overnight in the fridge. Makes the kibble smell more like hot dog without actually giving him the hot dogs.
Another alternative is freeze dried, single protein treats, like lamb lung or beef liver.
My dogs have pretty iron-clad stomachs but I've actually found freeze-dried liver to be the one thing that is most likely to give them diarrhea if they have too much, so I have to be very careful with how much I give them.
Similar to the hot dog-soak, I have had excellent success with cutting up a single strip of cooked bacon into tiny pieces, and then tossing them into a container of kibble (about 1.5 cups) and then microwaving it for ~30 seconds. Shake/stir it up when you take it out, and then let cool. I was really shocked when my picky, spits-out-kibble-in-training dog was happy monching down bacon-kibbles during training - in a training class, no less.
I also like to use steak/roast. I buy whatever is on the "last day" sale at the grocery store, trim off the excess fat, cook it up, and cut it into tiny pieces.