Cat grooming

I have several cats, all short hair so no high maintenance needs but I noticed a couple times a year they need more brushing than usual. My issue is I can't get them to stay on the table long enough. I give them treats to distract them and it works for a while but really like 15 or 20 minutes max unless I want to spend my monthly treat budget in one shot. I've asked the vet if I can give them a sedative but the vet wants to do bloodwork first and I can't afford that just to brush them. Anyone have any tips or advice on grooming cats?