In a revolver, I have tried round pieces of paper cut out with a hole punch the same diameter as the bullet base, glued on. I have also tried over-diameter paper rounds which would wrap up over the sides of the bullet as it was seated, kind of like a gas check. The third thing I tried was sizing and lubing normally (i.e., filling the lube grooves with regular lube), then dipping the base in Lee's Alox solution (tumble lube stuff whatever it's called) to coat the bottom and up the sides a bit, and letting it dry. The Lee Alox method worked the best. It made seating smoother. It cut down bullet base erosion significantly (nearly entirely, when examining recovered bullets), and eliminated leading (or nearly so, I don't remember exactly if it was ALL gone). I would also imagine that the bullet pull was more uniform, but don't remember checking extreme spreads and std. deviation as one method of verifying this. The paper checks had a tendency to fall off sometimes, and were more of a pain. But the Lee Alox is much cheaper than gas checks, which is why I tried it. One tube goes a long, long way.
I haven't tried any of this on a cast bullet for rifle, but would suspect it would help and would definitely be worth trying. However, as mentioned above, I have also heard that a gas check does more than just protect the base from gas -- it grips the rifling better than lead, reducing stripping. It is also tougher than lead, and can take more of a beating, possibly (partially) correcting an out-of-center lead bullet that has been beat up. This is just what I have heard, but it may just be someone else's uninformed opinion. Veral Smith says this in his book, but I don't know how he could know this for certain. Maybe he had a method that I haven't thought of?