But I don't want to restrict draw, as this is one of the issues I'm having (restricted draw).
Solo air flow is deliberately restricted to those 4 tiny holes you can see in the base of the heating element - jamming the stem right down can more or less completely block all air flow with the standard stem and the 4 larger holes in the stem itself don't look like they're going to impose much airflow restriction.
The physics of air flow are such that you can increase the amount of air flowing through those 4 holes in the heater cup with either more (negative) pressure or bigger holes. Drilling them out a little and voiding your warranty good and proper might work although I have not tried it but whatever you do, DO NOT let any metal swarf fall down where it could short the battery or circuit board!!
The extra draw people report with modified stems is probably due to external air bypassing those 4 tiny holes. I don't own a pvhes but from the photos at pv it looks like it looks like it allows a small amount of external air to flow through the rubber grommet down the 4 channels cut into the sides of the glass and back into the stem? That air bypasses the solo heater so MUST inevitably cool down the air going through the herb - presumably people using pvhes wind their solo's up beyond the 3 or 4 that works well for me with a stock stem?
My recipe for a DIY pvhes - try to loosen one side of your lips sealing around the glass stem to permit and control a tiny amount of fresh air to be sucked in?
It's hard to explain but easy once you get the idea. Pull one corner of your mouth slightly to the side while inhaling on the solo until you allow a tiny hole to form and let in some air - you'll probably hear a slight hissing and feel the easier draw. Note - this extra air WILL dilute your hits but will give a much easier feeling draw. Personally it's a compromise I can easily live with - I do it kind of automatically now as I finish the inhalation. I use a kind of goldfish mouth pull - like puffing a cigar as someone said until I can see the vapour starting, then a full seal slow draw about half way then a progressive slight loosening of one the corner of my mouth until I feel the draw free up a little to finish with a good long deep inhalation. Note I'm only diluting the last few hundred ml of the inhalation. In terms of hits, I find this works well for me. Technically, the last 150ml or so of ther draw (which in my case is diluted with cool room temperature air) does NOT get down to the gas exchange membranes in your alveoli where the THC and friends can be absorbed - it's called the respiratory dead space - all the air in the oropharynx and the trachea down to the 6th or 7th branch where the alveoli are -
http://en.wikipedia.org/wiki/Dead_space_(physiology)