Usually when you fire a primed case in a revolver the primer pushes back and makes it difficult to open the cylinder or shoot again. That could be a problem if your trainer didn't exspect it.
Inspired by the mounted cowboy shooters who use black powder blanks on ballons, I have made up "blanks" with smokeless topped with dry grits and capped by a well crimped thin cardboard wad. We used them to shoot ballons at close range without having to worry about cleaning the gun every day. They are not truely blanks in that the grits are expelled fast enough to penetrate paper. We were curious about how much power they had and tried one on a row of ballons. Five ballons were aligned in a row inside a distance of about 8 or 9 feet, and it popped them all. But I know from testing that a ballon is safe at about 18-20 feet, so there isn't much danger. If you want less mass coming out of the barrel you could probably push a wad against the powder and just fire that, but it might be a bit dirty since the pressure would be low. And the obligatory disclaimer, this information is what worked for me, I make no claims about how well it will work in your guns.
If you try it, consider that the blank rounds will be handled by lots of people, some of whom may not take great care since they are "only blanks". So I would make sure they were reliable and fairly robust.
PM me if you want any details.