Sorry I haven't looked back at the whole thread to refresh my memory, so forgive me if I am repeating...
do you try to help the wind out by tummy massage, cycling the legs or lifting legs up towards chest/face? My LO was and still is very trumpy, when they are so little they don't move enough to help the wind move do they? LO seemed to utterly love it when I lifted his legs, I'd lightly pat his bum (think Tracy recommends this) to give focus on where to push and we made games out of it doing trump sounds, blowing raspberries, gentle things at first but more up-beat as he got older, singing 'the wheels on the bus go round and round' (doing big circular movements with both legs) and 'the wipers on the bus go swish swish swish' (legs up at 90 deg to body and then swish from left to right) etc. In fact the rougher it is the more LO loves it, obviously always making sure they are not going to get hurt. We did trumpy songs and actions at every nappy change because the nappy seems to stop them bending fully.
We still do these at 5 months and he still loves having a trump and a giggle with me.