Modifying the absorption rate of nicotine won't mirror the sensation of a cigarette, it will only improve your addiction to nicotine. The nicotine is absorbed in the lungs, just not as rapid as being laced with urea/ammonia(nitrogen) If you really wanted to experiment, (although not advised) You could always
buy some GRANULAR lawn fertilizer, preferably one with high nitrogen, not any that is laced with weed control such as Scott's weed and feed. Look for a high nitrogen rate. Description is as follows. Say the granular rating is 25-5-5.....25% urea/ 5 is phosphorus/ 5 is potassium. The urea is bright white. Don't buy slow release, it's coated with lime. Add
one white granular to preferably a minimum of 100ml if you find the 25%. See what happens.........Again, I really don't recommend this. Really I don't.
Also to note, we're dealing with liquid. Once granular urea is dissolved in liquid or burned, it becomes a gas. So, not sure how effective this is. So it may take a different approach, such as crushing a granular urea into a fine powder, sprinkle some in the batting of a dry cart, then add liquid for immediate vaping, or good luck finding liquid synthetic urea.
Don't worry, commercial urea is not processed piss. It's synthetic, a byproduct of ammonia and carbon dioxide.
Dissolved urea must be kept cool and out of sunlight. If not, it will ammoniate........meaning your liquid will smell like piss, maybe even taste like it.
These reports show that farm stock have a fairly high tolerance of urea before DEATH.
But we aren't sheep and cattle.
Toxicity of Urea to Sheep
Urea and NPN for Cattle and Sheep
Here is a report that urea is already in our chewing gum at 3% and safe up to 300mg a day.....
798. Urea (WHO Food Additives Series 32)
Info on Urea Fert
http://www.extension.umn.edu/distribution/cropsystems/DC0636.html
Again, to each is their own. I'm not freebasing nicotine. If I feel the need to, I'll just go back to analogs.