Should I drill out pinhole leaks in cast iron drain stack before repairing with epoxy?
You know that you're dealing with a structurally-unsound pipe that could fail at any time, discharging the most entertaining sludge in the process. I'd be oh-so-very-careful not to disrupt its integrity. Drilling into it would count; I'd say even scraping and wire brushing could hasten its demise.

Assuming this pipe is under no pressure, then just about anything that adhered to the pipe would block the leaks. I would suggest using patches of good quality duct tape on the holes (if you can find them), followed by a wrap of electrical tape (stretched well) to hold it all in place.