Be careful, the experience may be of a different nature since there is suggestion of a weird kind of metabolism. Like it passes FPM first (unclear to me if that is relevant) then accumulates in the lungs, then in the brain. It's quite possible that IMing doesn't change much about this but then again maybe it does.
I have no experience with this but I wouldn't be surprised if a number of PDers do, in order to drastically shorten the onset time.