Well I would not recommend sprinkling a little on a joint and here is why - in a joint you will 100% burn all of the DMT. You are NOT going to find that to be a pleasant taste or smell.
Another issue is it takes minutes to smoke a joint.
You have about 30 seconds with DMT. Then you are smoking against a massive wall of tolerance. So even if you noticed a hint of body load or whatever with that first hit, by the time you got to the third or fourth, you would most likely just be noticing the foul flavor and odor.
But if you are 100% go on this I would say maybe add 25 to 30 mgs evenly to the joint.
Then light the joint and take a hit - maybe medium sized, and hold it.
Now just sit with it for awhile. Even let the cherry on the joint go out.
After a few minutes, hit it again. If you didn't feel much the first time or if you felt a bit and liked it, this time take two hits and maybe make them bigger. Hold them. Park the joint. Sit with it. . . .
You get the idea . . . .
Finally, expect SMOKED freebase DMT plus weed to be a rather harsh/caustic smoke, but I know you are my age and we old stoners have leather lungs so I'm sure you will be up to it.