I do it on our 06 getaway....there are multiple reasons for them not liking this...the Trap. wires are too long....like you i just adjusted the little rope part ..(sorry dont know the technical term)
second the wings werent designed for this...i think they worry about someone forgetting to put the pins in and having the wings collapse inwards....
third is the extra load on the mast
I'm 22 years old..and only weigh 150lb so Im not much weight...compared to my dad 220lb....he wont even dare to go out on trap...besides...we've found our fastest way to sail is me on trap...controlling the lines and him with is weight on the back steering...only problem is sometimes he gets crazy and has stuffed it into a wave once (we sail on the open ocean) and I took a trip around the mast...ended up sitting on the other wing seat

..so now im a little paranoid and i keep a VERY close eye on whats ahead.
sometimes i will climb over the wing and put my feet on the hull where they're supposed to be...but this is rare.