Take more, and do it in an empty, featureless room.
I find a strobe light can take an experience to a whole new level.
doesnt have to be empty or featureless, but this is on the right track.
move into a low light room, thats extremely comfortable, but isnt very visually stimulating. put on some softer, more natural music - like ambient music with sounds of animals or rivers or something, but with a fair amount of lower frequencies (Bass). again - nothing too stimulating, but just so something is there.
then do deep breathing exercises for an hour or so. tell your friend that if he successfully sits quiet and still long enough, performing breathing exercises, he will really raise the potential for a true transcendental experience on acid. if you dont know some good breathing exercises, look up a basic "3 locks technique" or some other breathing exercises on youtube. practice them for 5 mins while sober.
he might not dig the idea at first, but you gotta sell it to him. ive done this with many people, anyone with the willpower to sit quietly and do it has been changed immediately from a mere thrill-seeker to a much deeper, passionate person towards psychedelic experiences. besides, teh shit youll see on the back of you eyelids beats the pants off of anything youll see with your eyes open (and if you take it far enough, you wont know the difference between eyes open or eyes closed).
there are definite, scientifically quantifiable, cognitive effects from meditation exercises. doing these while tripping is mindblowing. im a very experienced tripper, and i never take psychedelics purely recreationally anymore. of course there is a recreational aspect, but i do it mainly to just practice breathing and letting my mind go. i can turn 1 single hit into the strength of 3-4 hits this way. 2 hits i can make as strong as 5-7 hits, except when i cease breathing exercise and favor trivial external stimulation, it goes back to being like 1 hit. you have be willing to let the mind go. the hallucinations and visions you will have are mindblowing. ive had full on out of body experiences in the woods in central park several times doing this, literally feeling my soul morph into the plants and streams and trees around me, again, on just 1 hit.
breathing exercises can make you "trip out" a bit on their own. while tripping, its a very powerful and extremely rewarding experience, and can show anyone disciplined enough that psychedelics have far greater value than just recreational potential.
some active breathing techniques:
i believe the name of this one is "celestial tour" and was developed by Daoists around 2000 years ago:
https://www.youtube.com/watch?v=l2xwi9vRAEQ
another variation:
https://www.youtube.com/watch?v=H0o-9qGWkz0&feature=relmfu
throat lock:
https://www.youtube.com/watch?v=8oOUJMvnwr8 variation of the "3 locks" technique. (this is actually one so powerful you can use it to stop bladed weapons from piercing ur throat)
basic breathing:
https://www.youtube.com/watch?v=QUF8tNJ-Z6s
theres hundres of exercises from hindu, daoist, buddhist, etc disciplines. just look them up and learn them. ones u can do while walking are really awesome when outside, ones u do while seated are handy for inside. im at a point where i couldnt possibly imagine doing acid without doing exercises like this, its much more boring otherwise.