Thanks for the quick response!
I suppose the JAA see the whole flight instructor/commercial pilot thing differently. In the US, a flight instructor who is getting paid to flight instruct is not considered to be excercising the priveleges of his commercial certificate, just the priveleges of the CFI ticket. Hence the need to only have a 3rd class medical etc..
So I guess getting paid is out of the question...however, does the CAA have the interpretation that just by logging flight time I am getting compensated and therefore excercising a privelege I do not have?