If you have a spring scale, you can use that to help set the drag. Set it for about 1/3 the breaking strength of the line. I'll check mine before I start fishing. Adjusting the drag during the fight is just asking for trouble. If it is set right in the first place, you are good to go. If you need a little more, on the hook set for example, your thumb on the reel will do the trick. I've seen guys with spinning reels do something similar by laying a few fingers over the spool.

Andrew