Here's what I do, I load up my dose in the bowl, take a few deep breaths, then I put the flame to the bowl and light up. But I only hold the flame there long enough to get the cherry glowing, then I take it away, I only need to hold it there for maybe a second or two, max.
When I "smoke slowly", I take one loooong slow hit, no toking, just a deep pull, into the bottom of the stomach, this comes close to clearing the bowl, il have maybe a small amount left to smoke on my secon drag. Dont hit it like you hit MJ, you must do it slower, so your getting more smoke into the bong and then when your lungs are nearly full, release the clutch(the little hole) and fill up your lungs with the changa smoke.
I never have to take more than two drags of the bong this way.
Also when I smoke weed through a bong, I just pile up the weed and toke, with changa I measure out the amount I want to smoke and then slow long hit.
It does'nt take much much flame to get your 100mg or so of changa glowing, thats when you take the flame away and pull slowly, making sure you leave enoung breath to clear the bong of all the smoke.
Two or three goes at it and youl have it sorted.
Let us know how it goes.